An old space battle cruiser flies. Within, a chubby co-pilot complains about their equipment being outdated. He wants to fight in battle again as his planet, Skonnos, once did over other planets. The more sedate pilot tells him soon they will have new equipment but until then they must not overload the computer and must use the backup computer. The co-pilot complains it takes too long to do it that way. They are 12 hours out from the planet Aneth and 12 hours toward Skonnos. The pilot tells the co-pilot they must be patient but the co-pilot tells him patience is for the weak. This is the last shipment of cargo for the Nimon, who has promised after he gets his cargo, to restore the Skonnan Empire; then they will get their war and battles using new ships. In the old days, a Skonnan ship was a feared thing before Skonnos's people began fighting among themselves. After leaving to check on the cargo -- a group of teenagers which he call "weakling scum" -- the co-pilot returns to the control room where he suggests they do the trip in 6 hours but then the pilot makes him change his mind to 9 hours. If they cut out the Dog Leg at Sector L75 they could do it in 9 hours but they must not overload the computer. The co-pilot sets it for 6 hours anyway. The ship can't take it and blows consoles. It starts to spin as the auto guidance dies. They can make it back to the right path if they can find the beacon. They bring the engines to full power but it causes a blast which kills the pilot and knocks the co-pilot down. The ship continues to spin in space.

With his hat on the TARDIS console as it moves up and down, the Doctor reads a manual about shutting down everything that can be shut down as he plans on making modifications to the TARDIS. Even though the Doctor shuts everything off, K-9 reports they are still moving, something Romana, when she enters in smart red riding jacket and gloves, confirms. And they are accelerating. The Doctor rambles about having turned everything off except what can be kept on. Romana asks him what he has been doing and he explains he was working on the control geometer, wanting to modify it. So, he has shut it off. Every time he says, "What could possibly go wrong..." something does and blasts come out of the console. Romana thinks they are in a gravitational field. The Doctor had to shut down the conceptual geometer and the dematerialization circuit. They look out the viewscreen and see blackness. Romana wonders if it is a black hole affecting them. The Doctor doesn't think it is a hard enough pull and wonders what it would feel like to be crushed to a singularity. He goes under the console where a blast turns K-9's head the wrong way round. The Doctor gives him mouth to mouth and turns the head the right way round. K-9 tells him he is all right. "Good, good," the Doctor says, only to find himself under more console blasts. It was only the defense shields. He tells Romana he can fix anything given time but Romana points at the spaceship outside in outer space which now comes into view. The TARDIS is heading straight for it.

On the Skonnan ship, the co-pilot calls Skonnos.

On Skonnos, in a strange dark city, black lycro wearing soldiers march up and down gangplanks and ramps. Soldeed, a bearded man with long cape and dark clothe, leader of Skonnos and the high priest of the Nimon, comes out from speaking to the Nimon and tell Sorak, captain of the Skonnos military that the Nimon himself has promised that Skonnos will rise with wings of fire with new ships. It is he who thought of getting the tribute from Aneth. The wild voiced man tells of a second Skonnan empire which will be born in order to conquer the other planets.

K-9 gets out a warning as the TARDIS hits the other ship. The Doctor claims the other ship has been here years or centuries. He extrudes the door, making a power path down to the door of the alien spaceship. Romana praises the Doctor for this and the three go down the path, K-9 and Romana holding onto the Doctor's scarf and he pulling them across the space bridge to the door. They find ball globes with sort of rectangular crystals in them. In the each crystal is hymetrusite which is radioactive. K-9 verifies this by giving them a reading of Q7.325 but the radioactive level is falling. The Doctor sends K-9 back to the TARDIS to check what can work.

The Doctor uses his sonic screwdriver to open a door, which opens upward by tilting. Inside are many teens, mostly blond males and brunette females. To alleviate their fear, the Doctor offers them a jellybaby. Seth is the only one to come forward and take one. Before he eats one, the Doctor has Romana show him how to eat one and that it is safe. The Doctor takes the one and gives Seth another and passes the bag around to each of them, one for each. When the Doctor calls Aneth a charming place, Seth asks if he has been there. The Doctor answers, "Yes but not yet." The Doctor and Romana figure they are caught in a gravity whirlpool, a kind of Sargasso Sea in space, the gravity drawing things into it. It seems as though someone were building themselves an artificial black hole using a fixed gravity beam. Romana suspects the gravity is increasing; it is as the Doctor tests it using his upraised foot and knee, dropping his foot down. A singularity is a mathematical point without dimensions, Romana tells Seth.

The co-pilot comes into the hold and tells them the teenagers are sacrifices. He points a gun at Romana and the Doctor but asks if the Doctor can get them out of this. He might. The co-pilot takes the two into the control room, calling the teens "weakling scum" once more. The Doctor says hello to the pilot but the co-pilot tells him the pilot is dead. He then blames the dead man for crashing the ship!

On Skonnos, Sorak doesn't know how to report the vanishing of the ship to Soldeed, who tells him to begin at the beginning and end at the end. When he gets it out to him, Soldeed must report it to the Nimon in the complex.

On the ship, the Doctor comes down from a ladder, having seen the engines above. It looks like old machinery fused with new machinery -- hodgepodge of devices. Romana comments, "Sounds like the TARDIS." The Doctor tells her the funny thing is that the new machinery should be incompatible with the old. As they talk, the co-pilot badgers them only if they can fix it -- over and over. The co-pilot behaviour brings the Doctor to ask Romana, "Have you ever noticed how people's intellectual curiosity sharply declines the moment they start waving guns around?"

Romana gets the idea to use the hymetrusite to repair it and use as fuel. She goes up the ladder to look. The Doctor must go to his ship -- the co-pilot protests but the Doctor has a suggestion -- let him have the gun and then he can watch himself. The Doctor offers Romana his sonic screwdriver but she shows him her own -- one which she built. He compares the two, calling hers a bit basic, then taking hers and handing his back to Romana! Romana calls for her own back and he switches them back. The Doctor goes to the TARDIS to get some gear. The co-pilot makes Teka and Seth get the Hymetrusite.

In TARDIS, the Doctor tells K-9 they up a gum tree without a paddle. The dimensional stabilizer is fused so the Doctor will have to use the gravitic anomoliser. K-9 gives him some info on Skonnos and its empire: a military dictatorship which once ruled over 100 star systems but were lost after a civil war on Skonnos.

Soon, the Doctor is up the ladder fixing the engines and giving them more power. He tells the co-pilot to wait for his signal before activating the ship. The gravity is making them all talk strangely and move slower. Romana will plug the anomoliser into the main circuit. The Doctor will go to the TARDIS and materialize it into the hold of the alien ship -- a dangerous move but K-9 has fixed the dematerialization circuit. Here, they can ride this out until it is safe. On his way back to TARDIS, the Doctor gives the teens more jelly babies.

Before the Doctor can get the TARDIS to the ship, the co-pilot gets his power and moves the ship away from the TARDIS. K-9 accidentally blasts part of the Doctor's finger, nicking it as they repair some more circuits in the TARDIS. K-9 tells him the gravity is increasing for the TARDIS. Out in space, rocks from broken up objects float nearby.

On the ship, Teka and Seth tell Romana that they never saw the Skonnan fleet but their relatives in the past did, saying that it once blotted out the sky. Romana claims that if the ships were anything like the one they are on, "a good shout would see the lot of them off." When she realizes the ship is moving, she blames the teens for not telling her but doesn't mind as she opens the door with her sonic screwdriver.

When the Doctor realizes he has been abandoned, he slaps the console hard, blaming the co-pilot.

Romana enters the control room on the ship and yells at the co-pilot, calling him a despicable worm and yelling at him to turn back.

On Skonnos, Soldeed vanishes off the platform, an odd way of his seeing the Nimon, and goes into the Nimon power room. The Nimon, a large alien creature with horns, a bull's head and body of a man comes to talk to him.

K-9 figures impact in 89.4 seconds. The Doctor tells K-9 they are about to know how a cricketball feels. The Doctor tells the old girl -- the TARDIS -- goodbye, telling her it has been a good partnership and tells K-9 he has been a good dog. He wishes K-9 would not say things like 58 seconds dead. The Doctor gets an idea from cricket.

On the ship, Romana tries to fly it back to the Doctor but the co-pilot makes her go back to the others in the other room. Angry, she bangs down her sonic screwdriver and leaves it on the console.

The Doctor spins the TARDIS off the asteroid and the TARDIS turns end over end, upside down. K-9 tells the Doctor there is no damage to either of their circuits. The Doctor tells him "good boy." The spin on the TARDIS made the asteroid kick it right out of the gravity whirlpool. The Doctor wonders to K-9 if he is wasting his time travelling around the universe saving planets when he would have made a great slow bowler (in cricket).

Soldeed goes to the Nimon in Complex and tells him about the ship being lost, blaming a possible attack on it by Aneth. The Nimon tells him to prepare a counter attack, telling Soldeed he is too idol. Soldeed tries to get some of the advanced technology to attack Aneth now but the Nimon will not give any until he gets all his tributes -- payment in full. Soldeed leaves the complex and tells Sorak that they must attack Aneth and get new sacrifices or find the lost ship.

On the lost ship, Teka tells Romana that Seth will destroy the Nimon who threatens to destroy Aneth if they do not pay tribute. Romana realizes she left her sonic screwdriver behind and can't get to the co-pilot.

On Skonnos, Sorak reports that the lost ship has been found. Soldeed tells him to prepare the ceremony.

Seth shares a private talk with Romana on the ship. He tells her of the Nimon who Romana deduces sounds like he has "an insecure personality complex." Skonnos became weaker due to the Great Civil War in which all died except the soldiers. Only the army survived. Romana says, "That sounds like a well organized war." Seth admits to Romana he is not a hero and doesn't want to be. He is just around by chance when things happen. He ran away from home and the king's people found him on the road. Rather than be sent back, he told them he was a prince, which he is not. The King believed him. Romana tells him he does have problems but promises that his secret is safe with her, "Cross my heart...both of them." The co-pilot gets Romana in to him to fly the ship down and calls the teens "weakling scum" again.

In the TARDIS, the Doctor has wires hooked up to the console which starts up but soon blasts into inactivity -- not to mention a lot of crazy wild sounds like pops and boings.

Romana is brought to Skonnos and before Soldeed, "I'm Romana--who are you!?" She wants to complain about the co-pilot calling him a creature. If she speaks again, Soldeed tells her he will have her eliminated. Soldeed questions the co-pilot who lies. He claims Romana and her friend were pirates who attacked him and killed the Captain! Romana tries to explain and tells Soldeed this man is lying. Soldeed knows this anyway and warns her not to talk again. He makes the co-pilot nervous and in the end, fires his spear at him to send him into the complex to be executed by the Nimon. Romana and the teens are to be sent next.

In the TARDIS, the Doctor does a countdown to console activation and it works. Now he must recover his gravitic anomoliser. K-9 tries to remind him of something else. The Doctor remembers, "And Romana, don't forget Romana."

On Skonnos, Soldeed addresses a forum of soldiers, young and old alike.

In the Nimon complex, the co-pilot finds himself in a maze. Worse yet: when he moves to follow Romana and the teens, he finds the walls change on him and he can't get to them... yet. He and the others, somewhere else, hear the roar of the creature.

Romana tells Seth if they can't find the Nimon he will find them; Seth tells her that is what he is worried about. Teka wonders how they can joke at a time like this.

The Doctor sees the Nimon complex from above and it reminds him of something but he can't tell what. K-9 reports a hemispherical defense shield of 7300 megazones. The Doctor wants to land unobtrusively... and lands in the middle of the Complex entry room. He exits the TARDIS with his hat on and sees two older men, clearly not guards but not responsive to his, "Good morning or is it evening here? Lovely day, isn't it? wasn't it?" Guards do come and point guns at him. "Oh no not again," the Doctor puts his hat in his pocket, "How is it where ever I go in the universe, there are always people like you pointing guns or phasers or blasters... take me to your leader."

In a new room of the maze, Romana's group find a yellow garbed husk of what was once one of the Anethian teens from a previous tribute... they are part of the tribute, too. The husk looks as though it has had the life sucked out of it. Teka touches it and it turns to dust. Teka is confident Seth will kill the Nimon.

The Doctor is brought to Soldeed and in Soldeed's office he notices a neutrino converter -- supposedly Soldeed's invention. The Doctor has seen similar things here and there. He tells Soldeed someone is building a black hole on his doorstep and he asks about Romana, a girl about so big, "always sticking her nose into things that don't concern her." Soldeed lies but Sorak comes in with the gravitic anomalizer, making the Doctor realize that Romana was here. Soldeed fires his spear at the Doctor but the anomalizer reflects the beam away from the Doctor, who runs out. He runs into a forum room where he makes a speech about wanting to "make this perfectly clear" and being "desperate to find the exit". So he joins the old men in a huddle, hoping they can tell him the exit, but inadvertently avoiding the guards who pass by. Once out of this room, however, the soldiers fire at the Doctor in the entry way of the Nimon Complex opening. Soldeed points his spear at the Doctor but the Doctor appears to jump into the Complex of his own will.

In the maze, the Doctor dishes out star stickers from his jacket pocket and puts them on the walls to be able to find his way back. The Doctor finds the walls change when the stars vanish and move with the walls.

The Doctor arrives, pulls out a red hanky and distracts the Nimon away using it and his coat. In the other room, it fires at him and he ducks. The ray hits a tube and a body of a teen falls out. Romana gets the dead co-pilot's fallen gun and blasts the controls on the wall, urging everyone out but only she, Teka, and Seth get out. The Doctor checks and then covers the body of the teen with the red hanky and runs out. The other five kids that were with Teka and Seth are trapped by the return of the Nimon. Romana, Teka, and Seth look for the Doctor.

Just outside the complex entry in the platform room, Sorak and Soldeed look at the strange TARDIS. It seems primitive on the outside yet it is advanced. From inside the TARDIS, K-9 watches the two of them.

In the maze, Romana, Teka, and Seth find a dead end and then hear footsteps. It turns out to be the Doctor who yells, "You call this a maze!? It's a cheat!" Romana urges him, "Shh!" The Doctor acts like a child, "Well, the walls keep changing!" He thinks the Nimon is using the tribute crystals to power a large furnace. Something evil and horrible is going on here. The Doctor then realizes the others are not with them... he wants to go back for the others.

The Nimon makes the five teens put their tributes into the power device.

The Doctor thinks they must go deeper into the complex. So his group does.

The Nimon shoots a non lethal yellow ray from his horns at one of the teens -- a dark haired boy who falls but is not dead. Soon, he and the other four are put into the tubes, in the suspended state.

The Doctor and Romana find a new room -- the power source room. It is a transmitter with the horns acting as an antenna. The Doctor sends Teka and Seth to stand guard. They ask what they should do if the Nimon comes. The Doctor says, "Ahh, tell me and then run -- in that order." The Doctor screams out to Romana, "Got it!" This is a giant positronic circuit which is why the walls of the maze keep changing as the circuits switch back and forth, open and closed. To find out where the transmissions are going, they need a computer. Romana suggests K-9 and the Doctor thinks he has it -- get K-9. He can follow their psycho spores. The Doctor blows the dog whistle.

In the entry room, Soldeed admits the TARDIS has resisted every attempt to open it and in frustration, bangs on it. The door opens and K-9 comes out, the door closing locked behind him. A guard shoots at K-9 so the dog zaps the guard down. Soldeed uses his spear to fire an electric blast at K-9 which stops the robot dog. Sorak finds he cannot get into the mysterious contraption -- the TARDIS is locked once more. They have K-9 taken to Soldeed's office-lab.

In the power source room, the Doctor thought this was a giant transmat but there is no path or pattern -- it is focused on the black hole. It could be a gateway through hyper space with the exit somewhere else. The Doctor tells her that when he mentioned the black hole to Soldeed, Soldeed didn't know what he was talking about. Romana nods, "Well, people often don't know what you're talking about."

In the forum room, Soldeed addresses old soldiers and talks of a new generation of Skonnan ships with each man present having his own fleet. The men cheer and again don't seem to know when to cheer, looking as befuddled as before. After the meeting, Sorak asks Soldeed what is in this for the Nimon. Getting something for nothing makes Sorak uneasy. Soldeed puts an arm around him and tells him he is too scrupulous. The Nimon may be brutal and powerful but he is simple -- Soldeed claims to have played fawn to the Nimon and put him on a long string.

In the maze hall, Teka hears the Nimon coming and asks Seth why he won't kill him. He will but not now. They warn the Doctor, who thinks K-9 came awfully fast. It is the Nimon. They all hide behind the various machinery. At one point, the Doctor wants to watch what intricate moves the Nimon is making on the machinery and is almost seen. He waves Seth, who wanted to help him and came out, back into hiding. The complex starts to glow red with power.

This signals to Soldeed and Sorak outside the complex, that the beginning of the Second Skonnan Empire has begun. Soldeed says, "Let the onslaught begin." Sorak tells Soldeed to take care as the madman leader goes into the Complex again.

In the power source room, the Nimon opens a wall panel which reveals a spiralling tunnel of energy which brings a small capsule to the small room behind the secret wall. He opens the capsule and greets two more Nimons to their new home, part of their Great Journey of Life. Crinoth is finished and the Nimons must migrate here now. The Nimons leave the room. The Doctor figures there are two black holes -- one on this end and one on the other with a hyper spatial tunnel in between the two allowing the Nimons to leap across the universe instantaneously. Once here, they will build more transmats and this is not the only planet that has been tricked. The Doctor must work on the device and send the Nimons back but if he touches the wrong thing, he could cause an explosion which could blow up the entire planet apart. The Doctor asks Romana to give him every bit of information about the capsule she can find. The Doctor sets off something which alarms Romana but is just the main power control. He can send it back now.

Romana finds herself in a dark place where a Nimon sees her. She runs.

Back on Skonnos, the Doctor moves to cannibalise an L circuit and some other parts to try to repair the damage Soldeed did. When Seth asks if there is anything he can do, the Doctor tells him he has helped tremendously already and pats his head. K-9 is what is needed right now.

In that other place, Romana, chased by two Nimons, finds a dead end near some body tubes -- the larder of the Nimon creatures.

The Doctor realizes his gravitic anomalizer can be used to fix the device -- maybe. If it is not compatible, he will cause a bang so big no one will even hear it. Soldeed slips out but the Doctor sends Teka and Seth after him. Teka has the gun and Seth has the spear.

Where Romana is, an old man in raggy clothes used his own spear to knock out the Nimons surrounding Romana. Sezom tells her his world is destroyed and all on it are dead. When she asks what happened, he says, "The Nimon happened." When he tells her his time is almost up as well, Romana helps him sit down. He calls her very kind. He caused the death of all his people, allowing the Nimons to come here. He thought they would bring peace, technology and prosperity to this planet Romana is on -- Crinoth. He thought a few tributes would be a small price to pay and he cries.

Back on Skonnos, in the maze, Teka is cut off from Seth when the walls change again.

In Soldeed's lab, Sorak puts K-9 back together again -- K-9's side was open.

On Crinoth, Sezom tells Romana the Nimons are like locust, swarming from planet to planet and their numbers are multiplying.

In the Skonnan Nimon complex maze, Teka finds her way to the Nimon's rooms and sees the body of the co-pilot laid out on a table. Once more having a strange urge to touch a dead body, Teka touches his face. She backs away into Soldeed who captures her when her gun doesn't work. He calls the Nimon, who arrives. Soldeed is shocked when two more Nimons flank this one!

In the power room, the Doctor gets the capsule to return but when he opens the door, proudly, he sees two Nimons, "Oh my prophetic soul!" He slams the door shut and sends the capsule back to Crinoth. When the Nimons come out and realize they are back on Crinoth, they wonder what happened. Also on Crinoth, Sezom and Romana, trying to get back to the capsule, hide in a small alcove as Nimon creatures pass.

In the lab on Skonnos, Sorak asks for a show of K-9's power. K-9 fires a warning shot at Sorak's chest, getting the man to put him down on the floor. K-9 leaves and the door closes. Sorak doesn't seem to be able to open the door to follow him.

On Crinoth, Romana and Sezom hide behind a nearly see through wall as more Nimons arrive in the hallway. They talk about a final contingency plan should their first plans fail -- blowing up Crinoth for extra power. There are still many Nimons on Crinoth but it doesn't matter -- the Great Journey of Life must continue. After the Nimons move on, Sezom tells Romana that the Nimons will convert the matter of Crinoth into extra power, using a chain reaction to destroy Crimoth's very substance. He also tells her he was given this spear by the Nimons but using Jasonite, he managed to convert the spear into a stunning weapon against the Nimons. Jasonite has electromagnetic boostering properties. He gives Romana some of the Jasonite and tells her they must use subterfuge to get back to the capsule. He distracts a Nimon as they move on and it shoots its horn's deadly beams at him. He rolls out of the way, falling to the floor and Romana stuns the Nimon from behind. Another goes to warn other Nimons and more start to come to the area. Romana is about to get in but a Nimon shoots Sezom down. She stuns the Nimon and goes to him, "Come with me." She can't leave him but he takes his staff back from her to hold the Nimon off, telling her to warn Skonnos and the rest of the universe. She goes as more Nimon arrive. She gets in the capsule, "C'mon, Doctor, come on!" The Nimon kill Sezom with another shot.

In the power room on Skonnos, the Doctor is surrounded by three Nimons. The lead one tells him, "Later, you will be questioned, tortured, and killed." The Doctor says, "Well, I hope you get it in the right order." He bluffs, telling them he was just admiring the view. Just as the Nimon on Crinoth blast away at the capsule, the Nimon on Skonnos brings the capsule back with Romana coming out, ready to argue with the Doctor. The Nimon move to kill her. Seth returns and Romana tosses the Jasonite to him, telling him to put it in between the poles. He does and shoots the Nimon down. The Doctor will turn the space time tunnel off but another Nimon arrives, its horns shooting at the spear tip, which throws Seth to the floor. As the Nimon tries to kill the Doctor, K-9 shoots it from behind. The Doctor diverts the space time tunnel and will send the Nimon nowhere in space. He sends Romana and Seth to the nuclear furnace and to find Teka. He will meet them there. Once there, they see Teka in one of the body tubes.

In the furnace control room within the Nimon complex-maze, Soldeed confronts them, calling Romana a meddlesome hussy. She tells him it is finished. He is quite insane now, telling her that the Nimon told him he was the last of his race but Romana tells him in reality, the Nimons are parasitic nomads. Soldeed moves to hit some switches but Seth uses the spear to shoot Soldeed who falls onto the controls which he manages to switch on, setting an explosion to go off which will destroy the complex. The Doctor arrives and orders K-9 to get the others and Teka out of the body tubes. Teka knew Seth would rescue them. K-9 follows the scent to the exit, having to compute a route as they proceed since the walls changed again. The red lights continue to blink, heralding the coming explosion. K-9 leads them to a wall and tells them it is the exit. The spear won't get them out. It is not a wall--it is an elaborate illusion. K-9 leads the teenagers out first, all of them seeming to pass right through the wall -- which wasn't really there.

In the entry room, Teka tells Sorak and other Skonnan men in black, that Seth is a hero. Seth tries to get her to stop this talk and tells them Soldeed is dead. Romana runs out, "Get away everybody, get away!" The Doctor comes out and passes her, "Quick, take cover! The whole place is about to explode!" Everyone runs out. The blasts knock the top off a building and destroy the Nimon complex in total.