On a sound stage somewhere in the desert near the city of Glasst, Lomas Alloran is frustrated by the continuing delays. The first recital is due to start in just a few moments and the acoustic reflectors still aren't in place yet. He urges his team to hurry up, as they're rapidly losing the light. One of the robotic Familiars confirms that they have optimum function on all peripherals, and Lomas switches on the microphone and begins to address his team. With the fading light illuminating the city walls, the sunset is perfect for the occasion, and from this distance the city could even be mistaken for a place of harmony, rather than a place of waste and suffering. For the last few months, Lomas has had to face criticism and scorn, but everyone here has helped him, and the only way he can repay them is to let them share in his performance. Eventually the recital begins and as the theme starts to develop, immortal, primal sounds can be heard. Several of the lamps in the lighting gallery burn out and Lomas tells a Familiar to replace them immediately, but there are no spares available so he gives the Familiar autonomous function and sends it out to find some. Suddenly the area is rocked by a terrible wind and the earth starts to shake, and Lomas and his friends begin to scream as the sound stage comes crashing to the ground.

The TARDIS materialises on a street by a canal, and the Doctor emerges, followed by Ace and Hex. His companions immediately complain about the smell, but he insists that it's just dampness in the air. It reminds Hex of a school trip he took to Venice where everything was wet and smelled a bit like rubbish, and though it pains the Doctor to admit it, Glasst City does have similarities to Venice. His friends comment on how the Doctor has a tendency to keep them in the dark and drip-feed them bits of information on a need-to-know basis, in order to make himself look clever and them look stupid. The Doctor denies this, but they think he enjoys making the grand 'reveal', although by that time it's usually much too late. On other occasions, the information he gives them is a bit misleading -- such as the trip to Breearos, where he said he just wanted to return his library books but they ended up staying for a fortnight while he negotiated the ceasefire in the Orbit Wars. Or Tau Sartos, where he said he wanted to use their reliable laundry service, but actually went to prevent the spawning of a Zylax swarm (which involved more mucus than Hex was comfortable with). Or Nydas 3, where he claimed... The Doctor interrupts his two friends and admits that this visit was supposed to be a surprise. He tells them Glasst City is a human settlement on the planet Nocturne about 790 years in their future, and although it's true that a war has been going on for a long time, he brought them here simply because it's one of his all-time favourite places.

The elderly composer Korbin Thessenger is struggling with his latest piece of work, and when the computer plays back his tune, he dismisses it as too awful to listen to. His frustration is not helped by a ring on the doorbell. Wondering who could be visiting him at this time of night, he orders his Familiar to answer the door and complains that he'll never get his work done with all these interruptions. However, he changes his tune when the robot introduces the visitor as his former student, William Alloran. Korbin can't believe his eyes and says he's been worried about the young man ever since he went to the front line 18 months ago. Will looks very dashing in his uniform, but he reveals he's on disability leave after he lost his left leg below the knee. Korbin himself has been busy trying to be creative and his rooms are littered with paper and musical instruments. His Great Mass is still eluding him, and although he now has the core of the material, he knows these things don't compose themselves overnight. Will asks about his brother, but Korbin is vague in his reply, saying only that Lomas is well and ahead in his studies, just as Will himself was. Korbin asks Will to play for him and the soldier reluctantly performs a refrain on the piano that he's been toying with. It's very rough, but he hopes to develop it into something one day, perhaps as a requiem.

As they walk through the city streets, the Doctor lectures Ace and Hex about the various art forms on this planet, calling it the Far Renaissance; he thinks there's something about loss and suffering that brings out the best in the human race. The war against a species called the Foucoo is a particularly futile and stalemated one that has already lasted 70 years, but this remains one of his favourite places because out of that adversity, there is wonder. He's seen it happen to a great many cultures over the years -- poetry, fiction, painting, music and art all blossom in response to war. He leads his companions up onto a bridge and points out the neighbouring systems of Tau Ceti and Zeta Reticuli, the Foucoo home system. Nocturne is smack in the middle, and soldiers pass through on their way to the front and come back this way when they're done or dead. It's grim, but it's also attracted to this city the greatest concentration of human artists and thinkers since the Florentine Renaissance. For a period of about 30 years, human art will flourish here in a way that will only happen half a dozen times in the entire history of the race, and it will become known as the Far Renaissance. The Doctor pays this place a visit whenever he gets the chance and he's even made friends here. He offers to introduce them to Ace and Hex, so they decide to take a trip to Ragpole's nightclub.

Lothar Ragpole is greeting the patrons at his salon when he finds his old friend Lilian Dillane sitting alone. He asks after Korbin and Luke, but she tells him they're too busy to come drinking, which she fears is a sign that they're all starting to get old. Ragpole is worried that by sitting alone, Lilian may be damaging the reputation of his establishment, so he sits down with her. He asks about her painting and she tells him she's working on a series of studies showing shadow and light on the canal. Ragpole himself has been busy with his latest epic, and he offers to read a few stanzas for her to lift her spirits. Lilian is too polite to turn him down and is forced to endure a lengthy monologue taken from Ragpole's eighteenth stanza from book nine.

The robotic Familiars report to Cate Reeney at the Overwatch and tell her that an acoustic anomaly has been detected at the central canal which may be associated with atmospheric disturbances picked up beyond the city earlier in the evening. Reeney thinks the waveform looks like a storm front, but there was nothing in the forecast so she has it run through the defence net in case the Foucoo are up to something. She contacts Nightwatch 16 and asks if they've noticed anything unusual, and learns that a stray Familiar has wandered into the area under autonomous function. She dismisses the incident as a false alarm, but asks to be kept informed.

The Doctor, Ace and Hex arrive at Ragpole's salon, just in time to stop him boring Lilian to death with the "worst poetry known to man". Ragpole is delighted to see him and they greet each other warmly. The host decides this is a night for celebration after all and Lilian, another friend of the Doctor's, agrees that his arrival is most timely. Although Ragpole and Lilian are looking a little older, they notice that the Doctor hasn't changed a bit since they last met, which is a change. The Doctor introduces them to his companions, and Ragpole notes that he hasn't brought along guests as feisty as these since he travelled here with Miss Jovanka -- and they all know how that evening ended! Ragpole orders a round of drinks for everyone and Ace is irritated to see that the Familiars are designed to look like girls. Despite Ragpole's assurance that people are more comfortable with robots in female form, she suspects it's more a case of male chauvinism. The Doctor advises his friends not to get too familiar with the Familiars, commenting that "a robot is a robot whatever it looks like". Lilian recalls that the Doctor has never been comfortable with them and he tells her it's because there's too much that can go wrong. He asks her how things are going in Glasst at the moment, and she says the artists' enclave is feuding and arguing as always, and then there's the war, of course. The Doctor recognises some of the old faces, including an artist called Octavia, but Lilian says they're not speaking to her at the moment as she recently renounced post-pigmentism. He also asks about Luke and Korbin, but Lilian says they're too occupied with their work these days. Ragpole thinks that this attitude is bad for the soul and inhibits the creation of art, which is something he's never suffered from as his establishment is the finest antidote. The Doctor tells Ace and Hex that Ragpole's salon has been serving the artistic enclave of Glasst for twenty years, but Ragpole fears it will not continue for much longer now that there are curfews and tighter restrictions in place. He suspects the new chief of the Overwatch has something to prove. Even this reunion will have to be cut short, as the law requires Ragpole to shut up shop in half an hour, so the Doctor suggests that they head for Korbin's rooms at Tanza's Palace and make it a private after-hours party instead. Ragpole offers to round up all the usual suspects and Lilian decides to stop off at Commune Square to see if she can rouse Luke Moray from his lodgings, but because she's worried about the dark pavements in the area, Hex offers to escort her.

Hex and Lilian hear strange sounds coming from further inside the house and although they can't make out what's causing them, they can feel a definite presence nearby. Suddenly they smell fire, and Hex tells Lilian they need to find her friend quickly before the building collapses around them.

Ragpole leads a group of rowdy revellers including the Doctor and Ace to Tanza's Palace, where the party can continue. One of the group is sent to ring on Korbin's bell while the others hang around the atrium. Ace is impressed with the building and the Doctor explains that it was once owned by the Lord Marshal, but it's now been divided into private apartments. The front door opens and the irritable Korbin Thessenger demands to know what Ragpole is doing here with all these people. Ragpole announces that they've come to visit him, and when Korbin refuses them admittance at this time of night, the Doctor steps forward and suggests they could always come back tomorrow instead. Korbin is delighted to see his old friend and now welcomes the entire group heartily into his house, offering them protection from the cold night air.

Lilian calls out to Luke, but there's no response. The entire upper floor is on fire and Lilian suspects some lamps may have overturned by accident. Hex demands that she fetch the Doctor while he continues looking for her friend. In the distance they can hear the emergency services arriving, but the smoke is making it difficult for Hex to continue the search. He's nearly knocked down by one of the Familiars, which is acting erratically, and then another robot from the Overwatch appears in the doorway and asks if anyone inside is injured. Hex tells it about the malfunctioning robot and orders are given for it to be restrained. Cate Reeney arrives on the scene and frogmarches Hex outside before he has the chance to protest.

Korbin asks the Doctor which face he's wearing for this visit and is pleased to hear that it's his current one. Korbin is genuinely pleased to see his old friend and admits that he's been feeling particularly friendless in recent months. His work on the Great Mass isn't going well and he wonders whether it'll be catalogued as an unfinished work in the future. He's guessed that the Doctor has foreknowledge of the future -- it's as if he has secret information but isn't willing to share it, even with his friends. He tells the Doctor that the war's going badly and the casualty numbers are increasing by the week. He says it sometimes feels like they're all being weighed down by a curse, but the Doctor's seen Korbin like this before and believes he always gets like this when his work isn't going well. Korbin asks the Doctor about the delightful Ace and points to her in the corner where she's being forced to endure one of Ragpole's odes. The Doctor notices that Korbin's favourite pupil Lomas also has his eye on Ace, but Korbin tells him it's actually Lomas's twin, Will. The Doctor remembers Will signing up and going to war, and Korbin explains that he only returned today so it's been quite a day for reunions.

Reeney escorts Hex into a cell and switches on a tape recorder. She explains that she's the Colonial Service Officer in charge of the Overwatch in Glasst City, which Hex deduces is the military police. Hex gives his full name and she checks for him on the database, only to discover that he has no papers, no permits or curfew passes, no civilian warrants and no means of identification at all. In fact, he doesn't appear anywhere on their census or immigration lists. Before she begins the interview, Reeney formally accuses Hex of murdering Luke Moray.

Will Alloran approaches Ace at the party and introduces himself. He tells her he's been away for a while at the front and she jokingly accuses him of using this as an excuse to chat her up. He explains that he uses it to explain why he's limping and she becomes embarrassed, but when she apologises for putting her foot in it, she just makes the situation even worse until she asks if she can start over again. Will tells her he and his brother were both awarded a bursary to study under Korbin Thessenger, but whereas he chose to put his duty first and join the military instead, Lomas was far less patriotic and stayed behind to finish his studies. When Ace discovers that Will's a musician, she asks him to play something for her, but then suddenly the power goes out and the room is plunged into darkness. The Doctor urges everyone to stay calm, but Ragpole starts to worry that it might be a raid. Korbin and Will assure him that there hasn't been a raid in years and if there was, they'd have heard sirens -- but then Ragpole looks out the window and sees a huge fire in the direction of Commune Square. The Doctor offers to repair the lights, but when one of the Familiars offers to show him to the power relay, he refuses to go with it and asks Korbin to accompany him instead.

Reeney records that the victim, celebrated composer Lucas Earthen Moray, died of violent causes at his home in Commune Square, and his body and his property was subsequently consumed by a fire. She confronts Hex with the fact that he was discovered outside the scene of the crime, and the evidence pointing to his guilt is fairly clear. As Hex is a young man, she thinks he might be a deserter from the war, as Nocturne is the last stop before the front line. Perhaps he jumped ship, ditched his papers and ended up living rough on the streets around the artists' enclave where opinions tend to be more liberal? She wonders if Hex thought Moray would have enough money to get him offworld, or perhaps it was just a simple burglary that went wrong? Perhaps it was a quarrel, or even a lovers' tiff? Was he really Moray's 'special friend'? Hex rejects Reeney's accusations, but he realises he's in a lot of trouble even without the murder charge, as the city is under military law and the punishment for not having correct and valid papers is death. Reeney produces a gun and threatens to skip straight to the execution. All it would mean for her is a shot to his temple and a bit of paperwork... unless he's ready to start volunteering information?

Korbin and the Doctor can hear someone moving around in the dark, and when the Doctor examines the power relay he discovers it's been shut off deliberately. He switches the power back on and the culprit is identified -- a robotic Familiar who's been removing all the lamps in the hallway. Korbin demands answers from the Familiar and it explains that it's working under autonomous function in response to an order to produce replacement lamps for a nearby campsite. He accuses it of theft, but the robot insists it is merely following orders. Korbin recognises it as Familiar 6, one of the units that was taken by Lomas. He orders it to go to the service room and place itself on standby. The Doctor wonders what Lomas is up to, and Korbin admits that the two of them had a serious argument the last time they met. He accused Lomas of being arrogant and unprofessional, the complete opposite of his brother Will. If he could have chosen which brother stayed behind and which one went off to fight in the war, he would have preferred that Will remained here. He feels Lomas is only interested in fame and is hungry for adulation. Lomas refused to complete the exercises Korbin set him, instead wanting to cause a big stir and cement a reputation for himself. Lomas has become obsessed with a theory about bio-harmonics, a word that clearly means something significant to the Doctor. Korbin says Lomas started studying ancient texts and buying strange apparatus. The next thing Korbin knew, he'd taken off with his bohemian friends in an attempt to realise his ambitions, pausing only to empty Korbin's larder and purse on the way. The Doctor asks if Lomas has studied alien sources to find out more about bio-harmonics and Korbin confirms that he used xeno-archaeological texts. Korbin admits that he didn't pay too much attention to them himself as he thought it was all awful atonal garbage. Just then, Will enters the hallways and Korbin wonders how long he'd been standing within earshot. Will tells the Doctor that Lilian Dillane has called and is in a bit of a state. She's at the Constabulary and says Hex has been arrested for the murder of Luke Moray!

The Doctor arrives at the Overwatch and meets Cate Reeney. He introduces Ace and Lilian and then asks Reeney to release Hex from custody. She explains that he's a suspect in a murder enquiry, but the Doctor and Ace emphatically insist he didn't do anything and this must be a mistake. Lilian claims Hex is one of her models and says he was accompanying her on a visit to Luke's home to invite him to a gathering. When they found the house on fire, she went to fetch the police while Hex stayed behind to find Luke. Despite Lilian's social status, Reeney has no intention of releasing her prisoner on her say-so and says she requires something more substantial. One of the Familiars then arrives with a report for Reeney, and after she reads it, she requests transport to be laid on and announces that she's releasing Hex from custody. The Doctor deduces there's been another murder, and Reeney admits that two women have just been killed and there are striking similarities to Moray's murder. As they leave, Reeney tells the Doctor she plans to keep her eye on him...

Will finds Korbin working alone on his composition and tells him that most of the guests have already left, although Ragpole is still hanging around. Will admits that he did overhear what Korbin said about his brother, and Korbin confirms that he has no idea where Lomas went. Will can't understand why Korbin didn't tell him all this when he first returned, but the old man says he didn't want to worry him. Will hopes it's not already too late -- the Ulanti might have understood bio-harmonics, but Lomas certainly doesn't, even though he knows it can be dangerous. Korbin insists he wasn't Lomas's keeper and didn't know Lomas was going to go off on his own as soon as his back was turned. Korbin and Will both become angry, blaming each other for what's happened, and Korbin insists that if Will hadn't gone off to war, he'd have been here to stop Lomas himself. Will turns and leaves...

As they leave the Overwatch, Hex thanks Lilian for sticking up for him. Ace is wondering what's going on here and the Doctor asks Hex to tell him again what he saw at Luke's house. Hex isn't sure what they saw as it was more of a ripple in the air, like a heat haze. Lilian insists there was something there and it made her feel dreadful, as if she was suffering the pain of a great loss. Lilian tries to describe what they heard, but Hex thinks it was more of a feeling than a noise. Although their description makes it sound as if nothing was there, Hex reminds them that the house was torn apart and Luke's body had been pulverised. The Doctor wonders if it could be sonic disruption, causing the atoms of the body to be shaken apart, leading to cellular collapse. It's a particularly nasty way to die. Hex remembers that one of the robots was having a funny turn too, like its brain had been scrambled. Lilian knows very well what the Doctor thinks of the Familiars, but she assures him none of them would have killed Luke. The Doctor points out that anything is possible, but in fact he agrees and suspects that whatever happened to the Familiar was just a side-effect of whatever killed Luke. The Doctor can't tell them what's responsible yet as he isn't entirely sure... except this obviously isn't turning out to be the holiday he was expecting. There isn't even the slightest sign of surprise on Ace's face.

Ragpole welcomes the Doctor and the others back and is pleased to see that Hex is unharmed. Everyone else has gone home as the news about Luke cast a damper on the party mood. Will is still around and has gone to the kitchen to arrange breakfast, so the Doctor suggests Ace gives him a hand. She realises she's being used to keep Will busy and the Doctor admits that he suspects that Will's brother is involved in this somehow, but until he knows more he doesn't want Will assuming the worst. The Doctor asks Ragpole if he could arrange some transport, and fortunately he knows someone who knows someone else who can get around the martial restrictions.

The Doctor finds Korbin tinkering in his workroom and tells him that Luke is indeed dead and currently "decomposing". Even though Korbin never regarded Luke as a friend, he mourns the loss of a real talent. The Doctor tells him Hex has been released without charge, but no one in this city is safe. Korbin thinks he's talking about the fire, but the Doctor reveals that it wasn't the fire that killed Luke. The Doctor asks where Lomas conducted his research into bio-harmonics, and Korbin assumes it would have been the city archive. He realises that the Doctor suspects Lomas might have something to do with the murder, and although they have no idea where Lomas is, they do know someone else who might know -- the Familiar that they caught stealing the lamps... In the service room, the Doctor and Korbin question Familiar 6. They unfold a large chart of the area and ask the robot to pinpoint the exact location of Lomas's campsite. It points to a location not far away, and the Doctor asks Korbin to take Lilian and Hex to the city archive to dig up everything they can on bio-harmonics while he and Ragpole go for a little drive in the country.

Ace joins Will in the kitchen and he offers her some coffee. He's glad she popped in to say hello and he asks if she'd like to go on a tour of the city. She readily agrees and they leave together. Meanwhile, in the Overwatch, the Familiars produce a report for Reeney containing the pathology results on the two women who were killed. While she reads it, she asks the robots to run a data-search on the Doctor. She finds the answers extremely interesting and orders the Familiar to locate the Doctor immediately.

As the Familiars move in for the attack, Reeney's voice calls out from the nearby ridge, ordering the Doctor and Ragpole to keep down. Suddenly the air is filled with weapon fire and one by one the robots are destroyed by Reeney's own Familiars. The dust settles and the Doctor congratulates Reeney on her excellent timing, but when he asks what brought her to this neck of the woods, she explains that she's come for him! The Doctor is confused, but she looks at the carnage around them and assumes he's been very busy. Ragpole laughs and tells Reeney she can't seriously believe they were responsible for what's happened here, but she hardly thinks the Familiars could have done it. The Doctor agrees, but reminds her that the robots weren't exactly being friendly either. Ragpole agrees that the Familiars do malfunction from time to time, but he's never heard of any actually attacking anyone before. The Doctor suspects their positronic brains were completely overwhelmed by an inrush of negative emotion that drove them insane. Reeney thinks this is nonsense, but the Doctor knows she felt the negative emotion herself when she arrived as he can see the fear in her eyes even now. It's an aftershock, an echo of what was created here in the Veldt...

Will begins his tour of Glasst City by taking Ace for a boat ride down the main canal. She admits that she's never been here before and he teases her for having a sheltered existence, especially when she tells him she originally came from Perivale, a place he's never heard of. He sympathises with her life of travelling and says he's experienced the slow crawl of transit times himself. It took him eight months to reach the war zone, and then he saw only four days of active duty before spending another eight months coming home again. He asks the robotic driver of the launch to take them to Ballardi Quay, and as they disembark, Ace asks Will whether he regrets going to war. He tells her he didn't, at least not until today. He remembers his brother Lomas laughing at him when he first signed up for action, and finds it odd that the two of them can be so alike and yet so different. Lomas was pleased when Will left as he no longer had to fight to get Korbin's attention. Will asks Ace where she wants to go first -- to the Museum of Culture or to the Lazlo Collection; after that, he'll take her to his favourite place of all, the College of Music.

Korbin takes Hex and Lilian to the city's archive and gives them a lecture about the building's origins. A robotic curator arrives and they request a full list of any holdings that make reference to bio-harmonics. It shouldn't take long to get the list, but then they'll have to start hunting for the specific volumes and manuscripts, and then they'll need to find a quiet reading room and begin studying. Hex thinks this is starting to sound more and more like his school trip to Venice.

The Doctor shows Reeney the acoustic deflectors, which have been crushed by an extreme force. He thinks they were part of a harmonic processor and the havoc they can see about them was caused by something manufactured by Lomas Alloran. He believes that Lomas was dabbling with an alien science he barely understood and that he released an unstoppable force that might still destroy the entire planet. He tells Ragpole the force is now somewhere in the city, which Reeney thinks is good because that's where she's taking her prisoners. She's had enough of the Doctor's fantasy and has decided to take both him and Ragpole in for questioning on suspicion of murder.

Will shows Ace a piece of art that's always been one of his favourites -- it's a statue called 'Man Triumphant Above the Rigours of Space' by an artist called Shumack. It took him eight years to carve from a single block of onyx and it includes a small creature by the left foot of the subject. Will tells her this is a representation of a Foucoo, but he doesn't know how accurate it is because neither he nor the artist have ever actually seen one. In fact, very few people have, as the Foucoo are subterranean burrowers and are aggressively territorial. Ace asks Will to tell her what happened at the front, and he tells her his battalion was deployed about 300 kilometres from the principal colony on Zocus. The mood of the troops was good as they were keen to see some action after eight months of travelling. They were deployed to some hills near a lowland forest, and on the first day a call came in alerting them to a patrol in trouble. Will's platoon, consisting of sixty men in armoured vehicles, was sent ahead. He remembers thinking that he needed to make sure he switched off the safety catch before firing as it would be really stupid to forget that. They reached an area where overnight bombing had opened up the ground and exposed some Foucoo burrows, formed of arches and tunnels made from wax or bone that were big enough to walk through. However, the Foucoo had mined the area with scattered micro-munitions that were set on delay so that the first people to trigger them would continue marching and the mines wouldn't go off until the third or fourth wave of troopers reached them. Will was in the front ranks and saw row after row of mines going off behind them, working their way forwards through the entire platoon and catching up with them. They ran, but the Foucoo were waiting on the far side. They opened fire and pinned the troops down until the exploding mines caught up with them. Will didn't even feel the one that ripped off his leg. He laid there for two days before he and the only other survivor were rescued. He'd gone to war but spent sixteen months travelling and only four days at the front, and never even had time to switch off the safety catch on his weapon.

The Doctor sarcastically congratulates Reeney on the charming cell in which he and Ragpole have been placed. He insists that he isn't the problem and that there's something in the city that will kill again unless they can stop it. Reeney tells him there were ten victims at the Veldt and the number of victims in the city has now risen to four -- a noted baritone was found dead in his practice room this morning. She demands to know what the Doctor has against the artistic community that would lead him to kill so many people, but he refuses to dignify the accusation with an answer. Reeney thinks she's dealing with either a Foucoo stealth weapon or with pro-Foucoo terrorists, and although she really needs help, the Doctor is the last person she trusts. She produces a document and asks the Doctor whether he'd trust him if their positions were reversed. The Doctor reads some of the research notes and concedes that she does have a point...

Will and Ace stop for a coffee in a café that's popular with the artistic set. Ace apologises for asking Will to dredge up unpleasant memories, but he thinks it's good to think of these things sometimes. His pet theory as to why Nocturne is such a focus for artists is that the place is so grim. It's a granite mausoleum of a city which towers over stagnant canals. Through the window they can see the Department of War, the munitions factories and the hospices for the crippled and the invalid. Everything here is about suffering, with horror and loss locked into the drab, bleak buildings. He thinks the artists' enclave is like a pressure valve, providing the only way to release the pain of the war. Music has been in Will's blood ever since he was born and it kept him sane on the long journeys to and from the front. He asks Ace whether Hex is all right and is shocked to learn that Luke Moray wasn't so lucky. Will didn't know the man personally, but he knew of his work. Ace reveals that the fire itself was just an accident and Luke was already dead when Hex found him. She says there was some sort of noise there, more of a feeling, which really shook Hex and Lilian up. When she tells him the Doctor suspects it was the noise that killed Moray, Will becomes distraught. He starts raving that his brother Lomas has done something and that it's all Will's fault. Without explaining further, Will leaps to his feet and races out of the café, leaving Ace alone and confused.

Reeney takes the Doctor through eight separate reports dating back over thirty years, and Overwatch documents mentioning the presence in the city of an individual known only as the Doctor, who was usually accompanied by one or two companions. There's not a scrap of paperwork to authenticate the Doctor's identity, but the Doctor says he doesn't like to stand on ceremony and he never admits to anything unless he has to. Whenever he speaks the truth, people tend not to believe him. Reeney accuses the Doctor of visiting the city illegally for a long time, but every time he comes here there's no record at all of how he gets in or out. To her, this sounds like the actions of a spy and she suspects he uses black market shipping or Foucoo covert operations, or perhaps he has someone on the inside on his payroll. The Doctor says he arrives here in a blue box that travels in time, but more importantly there's a deadly elemental force loose in the city that's growing stronger and more powerful with every life it takes. Soon it will be almost impossible to stop it. Reeney returns to one of the Doctor's earlier visits, about five years ago, in which two deaths were recorded that appear to have a connection to him, although the official records are mysteriously incomplete. The Doctor accepts that there was a cover-up but says this was because there was a Foucoo-sponsored plot to assassinate the executives of the War Department. Although the Doctor was only here to visit friends, he was able to lend a helping hand and stop the deeds from occurring. Reeney admits that the Doctor was right -- if that was the truth, then it's very hard to believe. The Doctor insists that he wants to help her and wonders whether anyone else has died during the time that she's been questioning him. He offers to make a deal. She should let him and Ragpole go and she can accompany them back to Korbin's lodgings to see what he has to show them. Only then should she decide what the truth is.

Hex and Lilian return with Korbin to his lodgings and check with the Familiars to see if there are any messages for them from the Doctor or Ragpole. There aren't, so the group settles down for some coffee and something to eat. Unfortunately they've spent the whole day sifting through manuscripts and they have nothing to show for it. Just then, the Doctor returns with the others, and when Korbin sees Reeney he assumes Ragpole has got himself into trouble again. Reeney apologises for the intrusion and the Doctor explains that he's hoping the team had a profitable day in the city archives and have something worth showing them. Unfortunately, the only thing they can tell him is that all works on the subject of bio-harmonics have been permanently deleted. The Doctor is intrigued and assumes Lomas had been covering his tracks, possibly because he was afraid of competition. Hex says there were plenty of references to bio-harmony, but nothing meaty, and Korbin says there was nothing at all about the Ulanti. The Doctor starts to become suspicious when he learns that Will was the one who prompted Korbin to remember the Ulanti. Perhaps Will knows more about his brother's work than anyone realised, but regrettably he had an argument with Korbin earlier and no one knows where he is now. Reeney believes the charade has gone on long enough and accuses the Doctor of dragging her here under false pretences. The Doctor ignores her and sends Hex and Ragpole to bring back Will as he might be their only chance of saving the city. Sadly, he also has to reveal that Lomas and all his friends are dead. The other artists are horrified by the terrible news, so Reeney agrees to let them collect Will, providing they aren't gone too long.

After searching for ages, Ace eventually finds Will playing the piano in one of his old school classrooms. He welcomes her and explains that this rehearsal room was one of his favourite places to study when he and Lomas were studying here. She asks him what he's playing and he tells her it's one of Luke Moray's compositions. Given the events that have happened, he feels it's an appropriate choice. He tells her it's not safe for her to be here, but she says she was worried about him. She asks him what he meant when he said he was responsible for Moray's death. Eventually he tells her that months ago, before he left for the war, he discovered in the archives some ancient alien scripts that were found on a distant planet. The archaeologists who unearthed them didn't understand their true significance, as it wasn't their field of expertise, but he studied them and discovered that bio-harmonics was a completely new kind of music. Pure, raw and beautiful, but potentially deadly. He realised he'd stumbled across dangerous knowledge and he erased it from the archives to prevent anyone else finding it. He thought that was an end to it, but his idiot of a brother was always trying to compete with him and he secretly made copies of Will's research on the Ulanti. Will only discovered what he'd done the day before he was due to ship out and they had a blazing row. He made Lomas swear that he wouldn't do anything with the information, but Lomas obviously ignored him and now it's too late. Will realises his brother has let something loose and in all probability it's killed him already. Ace tells him that the Doctor suspected something like this had happened, but he didn't want to say anything to Will until he was sure. She suggests they go back to Korbin's and talk to the Doctor, but Will refuses and says it won't do any good. He hands Ace his datapad, which contains all his compositions as well as everything Lomas copied from the research notes. In the meantime, he wants to wait here alone...

Hex and Ragpole haven't had any luck finding Ace and Will, and they meet up on the empty streets to exchange notes. Ragpole even went as far as the Lazlo Collection, but it was shut for the night. Hex found someone who recognised Ace's description who told him she was searching for a soldier and had gone off in the direction of the music school about an hour ago. Ragpole knows where the school is, but before they get very far, Ragpole hears a strange noise. Hex recognises the sound immediately -- it was the one he encountered at Luke Moray's house! Ragpole insists they leave straight away, but Hex refuses to go without Ace, so he races off alone.

Ace begs Will not to go too close to the noise, but just then, she hears Hex calling to her from the other side of the door. Will screams, and as the noise and wind fades away, Ace realises it's too late and her friend is dead. Hex bursts into the room and finds Ace unconscious...

Some time later, Ace wakes up and finds the Doctor leaning over her, concerned. He tells her not to get up and confirms that Will is dead. She tells him everything she's learnt about Will and Lomas, then she gives the Doctor the datapad research into the Ulanti bio-harmonics. The Doctor realises this information could save the lives of everyone on Nocturne. He's sorry about what's happened and although he knows she and Hex were only teasing him earlier, he now accepts they were right -- he takes them to places, but doesn't tell them why, or he doesn't tell them enough, or he only tells them everything when it's already too late. In his defence, he says he only does it to protect them and he genuinely brought them to this planet because he thought they'd like it. He didn't expect them to get involved in anything dangerous and he promises not to hold back information in the future. Ace wonders if Will would still be alive if the Doctor had told her what he knew, and the Doctor is forced to admit that he doesn't know. All he knows for certain is that Will Alloran, Thessenger's greatest and most gifted pupil, died too young and before he could fulfil his potential. The Doctor always assumed Will died in the war, which is why he was so surprised to see him back here, so perhaps he should have guessed sooner that things had started to go off the rails. Ace is also sorry as she knows the Doctor truly loves this time and place, and now everything has been spoiled. The Doctor decides it's time he sorted everything out...

Reeney confronts the Doctor, but he tells her to stay calm and points out that thanks to Will they now have the information they need. The datapad contains material from several reports made 200 years ago into the Ulanti and their homeworld. Reeney has never heard of the Ulanti, which isn't surprising as they've been dead for two million years, but the Doctor says that in their time they knew how to write a damn good tune.

Ace wakes up again and is pleased to see Hex watching over her. She tells him Will knew what was going to happen to him and he was deliberately trying to attract the noise with his music. Hex can't understand why he would do that, especially as it nearly got Ace killed too, but she says she could have left at any time. She thinks Will blamed himself for the fact that his brother created the noise and she in turn blames herself for telling him about Moray's death. Hex kisses Ace and tells her to get some sleep, assuring her that he'll be here for her.

Reeney demands to know more about the Ulanti, and the Doctor tells her they're a long extinct race who developed a technique called bio-harmonics. To put it simply, they used their own planet as a musical instrument and they were able to create music that was an expression of their own world, a natural melody produced by the biological rhythms of their own ecosystem. This was what Lomas Alloran tried to achieve here on Nocturne. Lilian thinks the idea of pure living music is beautiful, but the Doctor points out that while the Ulanti produced sublime music because their homeworld was a serene and an unspoilt wilderness, Nocturne is not so pretty. Reeney finds it impossible to accept that the killings in her city have been committed by a tune, but the Doctor explains that Lomas tapped into the essence of Nocturne and gave it a voice to cry out with. By unleashing the pain, the fear and the darkness of the planet, he was able to give it a form that's still growing in power even as they speak. Reeney doesn't believe the Doctor's theory, but Lilian finds it quite compelling. Thanks to Will's research, the Doctor is sure he can rig up something to stop it, but first they have to find it. What they really need is bait -- and Hex has something in mind, since Ace thought Will had attracted the thing with music. The Doctor realises that everyone who's died so far has been an artist killed during the act of making art, so this phenomenon may actually be drawn to art and beauty. It must be attracted to the antithesis of itself, so they can use poetry and music to lure it into a trap.

Reeney finally accepts the truth and agrees to help. The Doctor plans to reproduce the devices that Lomas originally set up and Reeney offers to contact the War Department to get the necessary equipment. Korbin sets off to clear the workroom so the Doctor can begin reconfigure things to Ulanti specifications. Once they're alone, Lilian asks the Doctor whether the noise really needs to be destroyed. Even though it killed Luke and the Alloran brothers, and nearly killed Lilian herself, she regards the living art to be something of value. However, the Doctor points out that even if was possible to install the noise in a museum, this particular masterpiece is deadly. No art, however perfect, should be valued over life. Lilian reluctantly agrees that there's no alternative -- it has to be destroyed.

A massive storm hits the city, a storm of such intensity that the Doctor is sure it can't be natural. He suspects the local climate patterns are being disturbed by the gathering power of the thing they're chasing. The longer the noise is out there, the more it's able to draw on the environment, so it must be frighteningly powerful by now. If it's not stopped, there's no telling what will happen after it's finished with Nocturne. As the Doctor continues working on the makeshift device, Korbin wonders what he should play, and the Doctor suggests anything tuneful or harmonious. Reeney arrives with all the equipment the Doctor asked for, apart from a loop modulator, but one of her techs suggested a pulse compressor might do instead. The Doctor is delighted and says he should be ready in another ten or fifteen minutes. Reeney confirms that a curfew is now in place and she has Nightwatch patrols out on every street from the Palladio to St Olaf's. She's also issued an injunction on all music, poetry readings and all forms of artistic expression, but obviously she can't guarantee everyone in the city will keep to it. The Doctor believes this will be enough to starve the noise and bring it here to Tanza's Palace towards the bait -- Korbin himself.

Ragpole, Lilian and Hex are waiting in the atrium. The Doctor and Reeney arrive and hand out communicators to everyone, then the Doctor asks if they all brought the pots and pans he asked for. He tells them Korbin is setting the bait upstairs to lure it into the compound, but it may need a little persuasion, so if they bang the kitchen utensils to make some harsh discordant sounds, the noise should be repelled just as much as it'll be attracted to the tuneful music. Their job is to spread out and make as much racket as they can around the edges of the Palace once they're sure the noise is inside. The Doctor tells Lilian, Ragpole and Hex to go anti-clockwise while he and Reeney will go the other way. Ragpole suggests they get the Familiars to do this part of the job instead, but the Doctor has already asked for the robots to be switched off as they don't want a repeat of what happened out on the Veldt. If the racket doesn't work they must improvise by shouting or stamping their feet, or possibly even reading some of Ragpole's awful poetry. Ragpole is outraged, but this isn't the time to argue and the Doctor decides to tell him his work is frankly abominable. Everyone agrees with his assessment and the poet is mortified, but the point is well made -- anything without artistic merit will do. As they go their own separate ways, the Doctor advises everyone not to whistle while they work.

The Doctor contacts Korbin up in the music room and tells him to start playing 'bait' music, so Korbin takes him at his word and begins a recital of 'Beethoven'. Ace enters the room with a yawn and compliments him on his choice of music. She looks over the Doctor's trap and thinks it seems a bit complicated, but unfortunately Korbin doesn't know how it works or even how to switch it on; he just assumed the Doctor would get here in time to operate it himself. He advises Ace to go and get some rest, but she wants to stay just a bit longer.

Ragpole, Lilian and Hex explore some of the corridors, but can't see anything unusual and head for the cloisters. Ragpole takes the opportunity to ask Lilian whether his poetry really is as bad as they said, but she tries to change the subject. Hex stops when he thinks he hears something, but the others assume it was just the wind. Elsewhere, Reeney suddenly realises she's alone with the Doctor and if he really is the murderer, this would be the perfect time for him to do away with her. Frustrated, he tells her to hold onto her saucepan and concentrate on the task. The Doctor comes to a sudden stop when he sees something move behind some doors. He tells Reeney to put her gun away, but she refuses. The doors open and one of the Familiar robots emerges and asks what it can do for them. Reeney is relieved, but confused as the robots were all supposed to have been shut down. The Doctor tells her to be quiet as he can hear the noise creature right outside...

The Doctor contacts Hex and tells him they've spotted something moving in his direction, but Hex says there's no sign of it yet. Just then, Lilian realises her heart is starting to beat fast and she starts feeling scared for no reason. Ragpole is also feeling terrified and wants to leave, but Hex tells them they have to stay as the creature must be very close. Hex spots a disturbance right in front of them and calls the Doctor to tell him they've found it, but something is wrong with the communicator. Panicking, Hex persuades the group to start making discordant noises with their pots and pans. The noise creature clearly doesn't like it, but continues coming towards them. Reluctantly, Ragpole decides the time is right to start reading out some of his poetry... The Doctor and Reeney race to join the others and find their way blocked by a locked door, but Reeney pulls out her gun again and shoots the lock off. They move through to the next corridor and meet up with Hex and Ragpole who tell them they were able to drive off the creature after all. Unfortunately Lilian ran off after it in the direction of the music room, where it's clearly being attracted by the bait. But with the communicators dead, there's no way to contact Korbin or Ace...

Korbin continues playing the music, but realises there's been no word from anyone for a long time. He wonders if the communicators have stopped working, but when he turns to look at Ace he sees she's dropped off to sleep after all. He finishes the tune, then moves on to another piece of music. Ace wakes up and recognises it as one of Will's compositions. She becomes angry and accuses Korbin of stealing Will's work, but Korbin assures her he has no intention of doing that. Suddenly a terrific wind bursts into the room, sending objects flying through the air. Korbin realises he doesn't want to be the bait any more and Ace calls for him to join her over by the windows. At that moment, Lilian runs in and pleads with Korbin not to let the noise creature be destroyed. The Doctor arrives and calls over to Ace, telling her to stop Lilian from getting anywhere near the equipment. He then confronts the creature and observes that it's built entirely from unremitting pain. He orders Ace to hit the switch, but in the confusion Lilian races forward and struggles with her. Eventually Ace is able to operate the switch and there's a tremendous explosion of noise and wind. Before long the sound dies down and the Doctor announces that the creature has gone forever, no thanks to Lilian, who's lying motionless on the floor. She appears to have a broken arm and concussion, but fortunately she's not dead, although that's more than she deserves. Ace asks him what the sound was that came from the machine and the Doctor explains that it was acoustic feedback modulated to echo and then cancel out the harmonics of the creature. The Doctor suggests moving Lilian to the infirmary.

Much later, Ragpole welcomes Korbin to his club. Although he isn't composing tonight, Korbin admits that he hasn't felt so inspired for years, which is odd really considering all that's happened. Ragpole asks why he's drinking here alone and Korbin tells him he needs time to reflect and to remember the good times. He was wondering if the Doctor might be here, but Ragpole shows him a note he found pushed under the salon door earlier this evening. Korbin reads the message: "Had to leave due to unforeseen circumstances. Take care until I drop in again. PS Don't be too hard on Lilian". Korbin ponders for a moment, then invites Ragpole to join him for a drink. He's delighted by the invitation, but less happy when Korbin asks him how his latest epic is coming along...