Wilf Mott is on his allotment, looking at the night sky and reminiscing about the events that led to Donna’s memory loss. His daughter Sylvia brings him a flask of tea and they remark on the absence of blue boxes in the sky. She persuades him to drive out to see Netty the next day, saying that the Doctor would want it, but Wilf refuses, even though he knows that she is right.
Several months earlier…
In the Oracle Hotel, the shining beacon of the Business District Development just off the M4 out of London, Terry Lockworth is fitting some extra-thin fibre optic wires into the new network system when the cables glow with a purple light. As he completes the last connection there is a bolt of purple energy and Terry is disintegrated, leaving only a few charred flakes. Upstairs in the penthouse suite, Johnnie Bates has linked all of the computers into the main server and is waiting to hear from Terry that his end is done. Johnnie is being watched impatiently by Dara Morgan, self made millionaire and owner of the Oracle. Morgan tells his PA, Caitlin, to tell Johnnie to connect his mobile phone to a terminal because cellular phones do not work in the service areas. As Johnnie does as he is told he, too, disintegrates. Morgan and Caitlin observe this death with quiet satisfaction and then turn to the rest of the staff, and to a ripple of laughter Morgan announces that the next day they will take over the world.
The TARDIS lands on Chiswick High Road. Donna and the Doctor are puzzled at how quiet it is for Friday, 15th May 2009 and remark that a Sunday in 1972 would be more likely. It is one month since the Sontaran stratagem was foiled and Donna wants to take her granddad out for a pint. It is also the anniversary of her father’s death, so she intends to spend a day with her mother. She arranges to see the Doctor the following day and heads off alone. The Doctor tells her that there is a flower shop called Loretta’s on the way but as Donna arrives outside Loretta’s launderette she gets a text message from the Doctor apologizing for his mistake, which puzzles Donna as the Doctor hasn’t got a phone.
Lukas Carnes is 15, hates technology, and does not have a girlfriend (blaming the latter on the former). However, since his dad left Lukas has been acting as a surrogate father to his eight year old brother Joe which is how he has come to be in Discount Electronics while his brother watches a demonstration of a fourth generation processor. He sees the Doctor using his screwdriver to speed up a laptop to phenomenal speed. The Doctor asks Lukas if the streets are so quiet because everyone is in the electronics shops and Lukas confirms this, saying that this is launch day. The Doctor notices that Lukas doesn’t seem that interested and the boy agrees before asking why the Doctor is there. The Doctor replies that he is there firstly to let a friend go home for a bit, secondly to see why everyone is in the shop and fourthly to because he is concerned about the new technology. Then he adds that thirdly he is there to save the life of Lukas Samuel Carnes before holding out his hand and introducing himself.
Dara Morgan is arranging with a Japanese banker, Mr. Murakami, to get the M-TEK out in the East by the Sunday, just two days away. Using a veiled threat to ensure the banker’s cooperation Morgan concludes the meeting to his satisfaction. As the Japanese leave Morgan tells Murakami that he needs everything in place by 3pm on Monday, UK time. Caitlin joins Morgan and together the couple remarks that on Monday Madam Delphi will have the planet and her revenge.
The Doctor and the Carnes boys are walking down the street. Lukas asks how the Doctor is meant to save his life and the Doctor produces his psychic pad. It reads: SAVE LUKASSAMUEL CARNES’S LIFE BY STOPPING HIS BROTHER BUYING AN M-TEK. The Doctor says he doesn’t recognise the handwriting. Joe points out that he was actually looking at a demonstration for a Psyrin Book Plus, though he concedes he did want an M-TEK. Waving off the boys the Doctor wonders when he last had a decent Italian meal. The psychic paper tells him SINCE 1492, which disconcerts him because the paper isn’t supposed to answer him like that. He also wonders what an M-TEK is and how Joe knew to call him ‘Doctor’.
Dara Morgan and Caitlin are in the Oracle penthouse looking at a computer screen, wondering why Madam Delphi is showing them a police box in a Chiswick alley. The computer tells them that it is a TARDIS and the three talk about the Doctor and Madam Delphi’s revenge on him and the universe.
In the New York office of MorganTech a major power failure causes every system from computers to air conditioning to go off. Melissa Carson leaves reception and heads down to the junction box in the basement. Not recognizing the ash by the box as remains of the maintenance man, she slams the box shut. There is a massive arc of purple light throughout the building and all 107 people and every other living creature in the building die instantly.
Madam Delphi gets around this problem by buying another software firm in New York. She sets in place plans to murder the firm’s CEO and then changes FBI records to show Dara Morgan as his sole heir and inheritor. She then books sub-contractors to install the new fibre optics in this new branch of MorganTech and the New York operation will be ready for the Monday deadline.
Back at home Donna is getting a hard time from her mother about being away, possibly dying, with the Doctor. Just as they fall into each other’s arms, tearfully, the Doctor rings the doorbell.
At an archeological dig in Moscatelli, Professor Rossi is having a hard time, too, preventing the interminable squabbles between three of his students: Sean, Ben and Jayne. Moscatelli is the professor’s home and he is trying to trace some tunnels through the local hills as well as track down the mysterious disappearance of a whole dukedom several centuries before. Suddenly his laptop brings him a message from Madam Delphi telling him that he has found the missing kingdom of San Martino. Wondering whether this is one of his students playing a prank he clicks onto a link and immediately absorbs purple energy into his hands. He tells his students and a local man, Tonio, that they have found San Martino. As they shake hands each absorbs the energy from the professor until all five turn to gaze into the sky and offer words of welcome.
Shortly after dinner in the Noble household, Wilf’s friend (‘bit on the side’ according to Sylvia) arrives. She is Henrietta Goodhart, a former astronomer who gave up working at the Greenwich observatory three years earlier and is suffering from Alzheimer’s disease. She introduces herself to the Doctor as Netty, a lively and gregarious lady. There is tension in the house: Sylvia is still seething over Donna’s trips with the Doctor as well as her perception that Wilf is trying to replace her mother with Netty. When the Doctor makes an unfortunate remark Sylvia slaps him and Wilf drags him out to the allotment.
Around the world more and more people are possessed by a purple energy. Some kill their loved ones; others pass on the energy and join together in looking at the return of an old star in the sky, offering welcome.
Wilf shows the Doctor a star he has discovered and which bears his name. The Doctor is more intrigued by another, brighter, new star near Orion. Wilf says it has been causing a lot of excitement and, according to the newspapers, is called a chaos body. The Doctor agrees to accompany Wilf to a dinner the following evening at the Royal Planetary Society to celebrate Wilf’s new star, then both men stare at the brighter star and shiver.
Saturday. Caitlin is wearing the uniform of Heathrow Airport Terminal staff, watching the big jets landing. Madam Delphi has supplied the all-clearance pass she wears around her neck. When she is stopped by a security guard who does not recognise her she disintegrates him with a bolt of energy. She collects passengers arriving from Greece, Italy and the USA, an army that Madam Delphi is building to end the human race.
Wilf, Donna and the Doctor take a taxi to the Society dinner. As they enter the dining hall Netty leads the assembled members in a sustained round of applause. As Wilf is congratulated, Netty and the Doctor converse briefly. It transpires that Donna has told Wilf about the Doctor’s true origins and Wilf has relayed the information to Netty. It seems, also, that only the Doctor and Netty have noticed the arrival of several more Chaos Bodies in the sky. The Doctor says the new ones are like satellites, but not manmade. He has a vague memory that he has seen something like them before. At the dinner the Doctor finds himself sitting beside the eccentrically dressed Ariadne Holt She gives the Doctor a frosty reception until the conversation turns to Chaos Bodies and the Doctor is the only one who can offer an explanation of the first one. He says it is a ball of superheated psionic energy forming a protective field around a malign intelligence. He says he encountered it in the fifteenth century and is worried that it has dragged itself halfway across the universe to be where it is. Naturally, only Wilf believes him, particularly when he names it as Mandragora.
The mention of the name galvanizes Madam Delphi into excitedly telling Dara Morgan that the Doctor is aware of her. Seven new arrivals in an SUV at Heathrow are galvanized into movement. The Japanese banker on a flight home realises too late that his M-TEK is sending him subliminal messages that he cannot counter. The Head of Hospitality, Gianni, at the Society, pauses while pouring a drink and whispers unintelligibly to Donna.
Later in the evening, the Doctor voices his concerns to Wilf. His last encounter with Mandragora was when it tried to stop the Renaissance, but now he can’t think of anything in Earth history that would have made it return. Then he remembers that Mandragora is a believer in astrology as well as astronomy and when Donna mentions that there is a Triple Conjunction between Neptune and Jupiter the Doctor realises that it will hit its peak at three o’clock on Monday, at which point the world will end. The Doctor and Donna jump in a taxi back to Chiswick High Road and the TARDIS.
In the Clemenstry Observatory, Western Australia, the new star is seen to be moving in conjunction with another. At the Copernicus Array in Essex Professor Melville declares this as unusual. The Array is situated in the gardens of an old Georgian mansion. News from other observatories around the world shows that the star is moving in conjunction with three other stars at least. When Melville combines the images of the stars a picture of a face emerges, a face wearing a malevolent grin. The professor immediately informs the Prime Minister. Then he calls the Doctor.
The call is taken on Donna’s mobile, re-routed from the TARDIS. The Doctor is not surprised. Shortly afterwards the professor and his assistant, Miss Oladini, are surprised by the arrival of a group of strangers. They talk about the two astronomers as ‘humans’. When they use purple energy to extract information from the old professor Miss Oladini runs for her life through the corridors.
The Doctor diverts the taxi to the Array. The lights are off in the building and the face in the sky is now visible to the naked eye. The group of possessed humans is waiting for them by the radio telescope and their leader greets the Doctor by name. He says that Madam Delphi wishes to speak to the Doctor and then uses a purple energy blast to knock the Doctor out. As they turn to kill Donna she runs back towards the house. An energy bolt narrowly misses her but blows open the French windows and she ducks inside. She slams the cellar door then hides in the office. Fooled by her ruse, two of the attackers go down the cellar steps while a third keeps watch at the top. Miss Oladini arrives as if from nowhere and pushes the sentry down the stairs. The two women introduce themselves as they run to the car park. They try to get into their attackers’ car but only just escape as purple energy smashes into it and the car explodes. Unable to find her saviour, Donna jumps onto a bicycle and pedals off quickly, disappearing into the night.
Fearing that Miss Oladini is dead, Donna cycles to the nearest town and takes a taxi home. Wilf is still up so she tells him everything before she goes to bed. When she gets up the next morning her mother is annoyed, thinking that Donna and the Doctor sent Wilf home on his own before going out clubbing. When Sylvia tells Donna that her granddad and the Doctor are up at the allotment Donna suspects that Wilf has gone to the array. She looks outside and sees that the car is missing and knows that she is right so she steals a van off the street and sets off for Essex. On the way she sees the malevolent face is still visible, even in daylight and there is a bright pillar of energy, purple at the edges, from the sky to the ground some twenty miles away.
The police have put a cordon round the energy beam which has turned a local wood to cinders. They find that similar pillars have been seen around the world. Seven people emerge from a gathering crowd and encircle the energy, joining hands and letting purple light pass between them until a sudden blast incinerates one of the police. The crowd stampedes away in panic. The police radios, which have been dead for ten minutes crackle into life. Madam Delphi announces that she is broadcasting to the world on every television, radio and computer and that the planet is hers. She adds that everyone connected to any version of Big Brother in the world currently being broadcast has just died.
Donna screeches to a halt as Lukas and Joe Carnes step in front of the van. They jump into the van and Joe recites the exact directions to the array. Donna wonders if he is an alien but Lukas tells her he is his half-brother, his father originated in San Martino. He says that Joe was given a free M-TEK when they visited a shop and some of his new found cognizance seems to have come from that.
Meanwhile, Wilf drives up to the Array where all seems to be quiet. He enters the house and comes across a fearful Miss Oladini. After the explosion the previous night she awoke in the bushes. As the night passed she crept into the house for warmth and hid in a cupboard. Now she has discovered the loss of her bicycle and just wants to go home. Instead she meets Wilf. Fearing that he is one of the ‘zombies’ from the night before she is relieved when he identifies himself as Donna’s grandfather and says he is looking for the Doctor. Miss Oladini has no idea who the Doctor is but joins him in the search. They enter the computer room and discover Professor Melville dead on the floor, his neck snapped. They discover the Doctor, unconscious, nearby and Wilf rouses him. The Doctor is saddened by Melville’s death and suggests that the Professor was used to align the telescope before being callously murdered.
The Doctor asks Wilf for his phone but is told that its battery is dead. The Doctor recharges it with his screwdriver and gives it to Miss Oladini. He tells her to go home and not to answer the phone when it rings but to simply press the hash key. Shortly after Miss Oladini leaves Donna arrives with the two boys.
In the Oracle Hotel Dara Morgan and Caitlin are listening to Madam Delphi exulting in the demonstration of her powers and proposing the figure of sixty percent of humanity being in her power when the M-TEK goes on sale later that week. Dara Morgan, however, seems to be distracted by a vague memory.
The Doctor tells Wilf and Donna that he encountered the Mandragora Helix in 1492 in Italy when it was trying to prevent the Renaissance. The Helix was an alien entity from the Dawn of Time that he accidentally brought to san Martino. He buried the fragment after he defeated it but now realises that it has spent the centuries permeating the soil and creeping into the DNA of those who lived on the land. As they and their descendants spread through the world they carried their DNA further afield. It is these descendants who have been awoken by the Helix and it is they and others under their control that are emerging as Madam Delphi’s army.
In the van back to London, Wilf sits up front with Donna and the Doctor talks to the two boys in the back. Joe shows his M-TEK to the Doctor, explaining that it combines an MP3 player, phone and movie player with internet capabilities and super-fast computing. The Doctor tries to shut it down with his screwdriver but fails. Even a blow from a hammer fails to dent it, which he declares impressive but also impossible. They drive up to Greenwich through deserted streets and stop outside Netty’s house. She joins them in the van, asking if they have seen the news. They haven’t so she tells them to drive through central London. They see nobody on the route, apparently the Prime Minister warned everyone to stay indoors. But when they arrive at the Embankment they find a crowd, a million people, arms raised and chanting, ‘Helix! Helix!’
The Doctor tries his screwdriver again on the M-TEK, attempting to alter some of the programs but accesses a horoscope site run by Madam Delphi. Lukas tells him that she is published in MorganTech’s newspapers but when the Doctor professes ignorance Lukas tells him about Dara Morgan and his global media empire. When Lukas says that a million M-TEKs were given away free the previous week the Doctor surmises that all of the recipients were of Italian descent.
They decide to make their way to Morgan’s base by an alternative route due to the huge crowd but as they leave the van they are confronted by the seven people that were at the Array the previous night. The leader, a man of Italian descent, demands to know how the Doctor interfered with the M-TEK. The Doctor offers to get the device from the van but the Italian climbs in through the doors and the van explodes, killing him instantly. The Doctor is less than impressed with the extreme and murderous Mandragoran way of doing things but understands that an M-TEK that has been tampered with would be a weak link in the chain.
The six survivors lead the Doctor, Donna, Wilf, Netty and the two boys through the streets. On the way they pass many groups chanting to the skies. On the way the Doctor links arms with Netty and begins to talk to her in a voice so quiet that even Donna cannot hear the conversation. After a number of rests they take a break in a deserted burger restaurant where Netty seems to write something for the Doctor. After each rest they are led on by their captors despite the growing exhaustion of the boys and the older couple. Midnight approaches while they walk through Chiswick and a mini-bus stops in front of them. Caitlin steps out and says she has come to take them to Madam Delphi. Donna grumbles that they could have been picked up three hours earlier but Caitlin explains that Madam Delphi prefers tired prisoners. She then announces that it is Monday, the day the universe changes forever.
They are led up to the penthouse by Caitlin. The Doctor starts to cap slowly at what he sees. He greets Madam Delphi/Mandragora when he sees the computers. She greets him as a Time Lord. They are joined by Morgan and the small group of converts. The Doctor reminds Mandragora of how he won their last battle but she points out that the Helix has been to Earth since. The Doctor lists The Sacred Mountains of Xi’an, the Orphans of the Future and the Mandrake nightclub, but says that was only a fragment of the Helix each time. He asks why Mandragora used the psychic paper to get in touch with him. He says that Dara Morgan is an anagram of Mandragora and tries to see into Morgan’s mind to find out who he was. He finds a man called Callum Fitzhaugh who was struck by purple lightning on a lonely walk home after a proposal of marriage had been turned down. The moment the lightning struck he started the transformation into the multi-millionaire Dara Morgan, building a computer system according to a voice in his mind and adopting a lifestyle based on a fictional past that had become more real than his true story. Years later in Dubai he encountered the girl who had turned him down: Caitlin.
It takes a second to retrieve this information, after which Morgan collapses to the ground. The Doctor asks for Donna’s phone and dials Wilf’s number. Donna sees the way that the Doctor is looking at Netty and realises he needs something from her but the old woman seems to be having one of her ‘moments’ and has become detached from the scene around her. Madam Delphi orders her converts to destroy the Doctor’s friends but when they raise their arms to fire their bolts of energy…nothing happens. The Doctor says that Miss Oladini has knocked the alignment of Mandragora’s energy off, cancelling her power over her converts. At the same moment, Dara Morgan is using a laptop to send a cancellation signal to M-TEKs everywhere. Caitlin pulls out a revolver and shoots him in the head. The converts flee in terror and Donna tells Lukas and Joe to go with them. The Doctor asks Donna to follow, saying that the newly unconverted people in the hotel will be feeling confusion and panic and will need her calm head to help them.
Caitlin slumps by a computer, saying that she feels guilty for what she has just done. The murder happened with no prompt from Mandragora, although she feels Morgan had done enough to warrant death. As she talks she creates a virus to slow down the alien, then takes the Doctor’s screwdriver and plunges it into a junction box. The Doctor shouts to stop her, but too late. There is a purple flash and the girl, the box and the screwdriver are reduced to atoms. The Doctor tells Wilf that the computers are off line so they have three minutes to overcome the Mandragora energy in the room before it finds a new home. They both look at Netty. Wilf objects but the Doctor produces a note Netty wrote earlier asking Wilf to trust the Doctor. As they speak, the energy passes into Netty who immediately begins to make threats against the universe. She says how wrong they were to try to stop human progress and should, instead, have allied their power with the humans to create an empire among the stars.
Donna returns just as the Doctor begins to explain to the Mandragora that it has been tricked. The process of moving into Netty’s body has speeded up the effects of the Alzheimer’s. As the Doctor and Donna fire questions, rapidly, at the ailing woman she loses the ability to think. Wilf can stand it no longer and begins to sing a familiar song that Netty once sang with her husband in her youth and Netty, stumblingly, joins in. With a scream a bolt of purple energy flies out of the old woman and through the ceiling. Mandragora has gone. Netty suddenly returns to her more lucid self.
Out in space the Mandragora Helix searches for home, its mind unraveling until it fades away.
Down in the canteen the army of converts become themselves again, some of them perplexed to find themselves in England. The Doctor sends them all back to their lives. Donna asks what will happen to them if they did something bad in their home countries while they were possessed and are wanted on criminal charges but the Doctor says that he can’t sort everything out.
UNIT tidies up the MorganTech mess, recalling all of the M-TEKs.
At the Noble house there are reconciliations: Sylvia offers to let Netty move in; Netty says she knows her new lucidity is a temporary reprieve and that she wants their help to find a suitable care home; Donna offers to give up her travels in the TARDIS before her mother finds out about them; Wilf demands that she continue her adventures.
Wilf is on the allotment at night, in the rain. Sylvia brings him a thermos of tea. It transpires that neither of them has been to visit Netty. They talk briefly, about Donna and her life after her adventures with the Doctor. They also discuss their fears about the world and who will protect it now that the Doctor has gone from their lives. Sylvia gives Wilf a letter that Luke delivered by hand that afternoon. Wilf reads it. It was written by Donna, to her mum and explains the truth of all the things she has done with the Doctor. It was written six weeks earlier. After he has read it Wilf looks at the skies and wishes that the Doctor would return, not just to save the world, maybe just for a cup of tea.