An emergency symposium of the Falsh Industries Select Executive convenes aboard a conference podule in orbit around Saturn to discuss the “accidental” destruction of the Jovian moon Carme. Most of Jupiter’s moons are scheduled for demolition, but the test detonation should have occurred on Callirrhoe; Carme was one of the Ancient Twelve, marked for preservation, and the “Old Preservers” who oppose the demolition on behalf of the Empire Trust are furious. Senior executive Cinnamin Tinya has arranged for Blazar Demolition to be blamed for the mix-up, and has reassigned the demolition contract to NewSystems Deconstruction, one of Falsh’s subsidiaries. Aristotle Halcyon, the artiste responsible for the forthcoming orchestration, will no doubt be upset that his careful artistic calculations have been disrupted, but Falsh has arranged to mollify him by paying him off with a collection of antiques.

The top-secret meeting is interrupted when the executives discover two men hiding under the table: the Doctor and Fitz, who have been searching the podule for spare mercury with which to repair the TARDIS’ fluid links. Falsh contacts security, and the Doctor and Fitz are split up when they flee. Fitz finds his way back to the loading bay where the TARDIS materialised amongst the crates containing the antiques promised to Halcyon; they are being loaded aboard Halcyon’s ship, the Rapier, by floating robot magnetic discs. Fitz gets into the Rapier before Falsh’s guards seal off the landing bay, and discovers that the TARDIS has also been loaded on board; however, Trix is no longer inside, as she presumably grew bored and wandered off to explore on her own. While searching for her, Fitz finds a room with walls glowing in psychedelic colours -- and when he touches the wall, his hand begins to glow as well. Suddenly feeling unwell, Fitz stumbles into another nearby room and passes out.

Trix is in fact aboard the conference podule, where she disguises herself as a waitress to avoid security and ends up serving food to the executives in the boardroom. Halcyon and his PA, Salsa Sook, are upset about the destruction of Carme, but Tinya and Falsh convince the reluctant artiste to take this opportunity to construct a new and better version of the moon. Falsh then shows Halcyon the infomercial his company has prepared to advertise the forthcoming extravaganza, and Trix watches it as well and is thus brought up to speed.

The Doctor evades the security patrols by hiding in the kitchens, where he finds a room full of “chiggocks,” genetically engineered food animals like walking plucked turkeys with no central brain. He then finds his way to Robart Falsh’s office, intending to use the podule’s security monitors to track down Fitz. He arrives just as Falsh’s secretary, Nerren, is leaving -- but Tinya then arrives and catches him. The Doctor assures her that he just wants to recover his blue box and leave, but she doesn’t believe him; however, Trix arrives and knocks her out before she can turn him in to security. Trix explains that Tinya left the meeting early, claiming that she was going to check that the antiques had been loaded aboard Halcyon’s ship, but she instead sent Nerren to do it, apparently so she could slip into Falsh’s office for reasons of her own. Unfortunately, the antiques have indeed been loaded aboard Halcyon’s ship -- including the TARDIS, and presumably Fitz with it -- and Halcyon is preparing to leave.

The Doctor and Trix rush to the landing bay, but arrive moments too late and are sealed inside as the Rapier prepares to blast off. At the last moment, they find shelter in Robart Falsh’s personal shuttle, the Polar Lights, which is also prepped for launch. The Doctor takes off after the Rapier, and as he tries to bypass the ship’s navigation and security systems, Trix brings him up to date. The human race has gone through the solar system like locusts, strip-mining the minerals from the planets and using the resources to establish an interstellar empire. The now-worthless solar system has been all but abandoned, but in a bid to lure back big business, Falsh has created a network of orbiting conference podules -- FILOC-Ps -- and he and Halcyon are “tidying up” the solar system, using the principles of Feng Shui to make it less cluttered and more spiritually pure. They have already sold off the asteroid belt and the Oort Cloud, and are now about to destroy most of Jupiter’s smaller moons, leaving only the Ancient Twelve.

The Doctor overrides the Polar Lights’ security systems, but is forced to burn most of its fuel in order to get away from the conference podule’s security probes; unfortunately, he loses track of the Rapier while doing so. However, from what he overheard in the meeting, Falsh and his executives are actually responsible for the destruction of Carme -- possibly for the insurance money -- and they’re taking steps to ensure that the truth does not come out. The Doctor thus decides to visit Blazar Demolition’s HQ on the Jovian moon of Thebe, find evidence to prove wrongdoing on Falsh’s part, and blackmail him into helping them find Fitz and the TARDIS.

Falsh finds Tinya recovering in his office, and she claims that Trix forced her here at gunpoint. For reasons of his own, Falsh doesn’t want anyone checking the security logs for undetected arrivals on the podule, and he thus does so himself, firing the current security chief for incompetence. A chance comment by another executive reminds Tinya of the Doctor’s claim that he just wanted to leave in his blue box, and she easily convinces the inexperienced new security chief to let her look at the security tapes. She thus sees the TARDIS materialising from thin air and subsequently being loaded aboard Halcyon’s ship.

Fitz is caught aboard the Rapier by Sook, who demands to know how he got on board and why his hand is covered in wet Halcytone paint. Embarrassed by his overreaction, and irritated that Sook seems to think he’s a wannabe art student, Fitz claims that he could be anybody, even one of the “Old Preservers” that Falsh had mentioned. As Halcyon approaches, Sook orders Fitz to prevent that he’s an art student as she suggested. Halcyon -- who is looking oddly at Fitz, but apparently fails to notice his glowing hand -- wearily agrees to check out his work. Fitz first washes the paint from his hand, and Sook is surprised to learn that he’s never heard of Halcytone, which is embedded with nano-optic fibres that change the paint’s colour as it dries. Halcyon invented it, and Falsh acquired distribution rights and had his scientists improve the formula. Sook begins to suspect that Fitz isn’t the person she thinks he is, but she takes him to the artist Roddle nevertheless to prove his artistic prowess on a PadPad template. To Fitz’s surprise, Roddle is clearly crazed on hard drugs, which are perfectly legal in this era -- and to Sook’s surprise, Fitz has no idea how the PadPad headset works. Once he grasps that he just has to use his imagination to furnish and design a blank flat, he finds it surprisingly easy, and he creates a number of dwellings based on his past experiences on Mechta, Yquatine, and the Council of Eight’s space station. But it’s clear to the appalled Sook that Fitz has no classical design training and was just making it up as he went; now it will be clear to Halcyon that Fitz is no artist, and Sook will be blamed for letting him on board. As Sook storms off, Fitz finally notices that something’s poking him in the foot, and discovers that he’s had the TARDIS key hidden in his shoe all along.

While examining the Polar Lights’ security system, the Doctor finds partially deleted footage of Tinya searching through Falsh’s personal belongings. The ship then arrives in Jupiter’s orbit; tourist ships are flocking around Callisto, awaiting the spectacular detonation of the Jovian moons, but the Doctor picks up another ion trail heading for Thebe. He and Trix arrive on Thebe and enter the Blazar HQ through the storage bay, but they are attacked by an alien like a humanoid fish in a spacesuit. When the Doctor tries to escape by climbing over a crate, the alien uses a remote control to activate one of the floating magnetic discs and pull the crate back; however, the Doctor uses his sonic screwdriver to interfere with the signal, and the crate drops, causing the others to topple in a domino effect. The alien is injured when the crates fall on him, and is forced to retreat, leaving the Doctor and Trix alone.

The Doctor and Trix then discover that the Blazar crew have been tortured and killed, presumably by the alien. They find a single survivor in the computer bay, a man whose nametag identifies him as Chief Supervisor Torvin. The shaken Torvin claims to have no idea why the alien killed his men, but when the Doctor examines the footage of Carme’s destruction, he discovers that a supposedly abandoned business complex launched itself into space moments before the moon exploded. The complex is still intact, but is on a decaying orbit that will eventually cause it to fall into Jupiter. Torvin shows little interest, and flees, claiming that he intends to hide out in an unfinished FILOC-P near Pasithee until his friends can rescue him. Ships from NewSystems Deconstruction then arrive with orders to destroy the moon, but the Doctor and Trix flee back to the Polar Lights and escape moments before Thebe is destroyed, along with all evidence of wrongdoing on Falsh’s part.

Fitz leaves the stone Roddle sleeping in an empty room and finds his own way to the cargo bay; to his surprise, Sook emerges from the darkened hold, giving him the opportunity to slip inside. He confirms that Trix is no longer inside the TARDIS, which means he must find a way back to his two friends -- but when he emerges from the TARDIS to plan his next move, he is tackled by two strangers, Gaws and Mildrid. Sook returns and helps the two to overpower Fitz, but reveals that Halcyon now believes Fitz to be an artistic genius, and Fitz realises that being reconstructed by the TARDIS has given him an affinity with virtual realities such as the PadPad template. Gaws and Mildrid reveal that they are Old Preservers who intend to prevent the destruction of Jupiter’s moons; Sook is helping them, because she believes that Halcyon is debasing the principles of Feng Shui, which she taught to him. This is why she helped Fitz earlier, when he suggested that he might be an Old Preserver himself. He now claims to be an part of an investigation team looking into corruption in Falsh Industries, and Gaws and Mildrid, impressed, reveal that they have a plan to blow Halcyon out of the water -- but don’t go into details.

The Doctor pilots the Polar Lights to the complex that was launched from Carme. Due to the minimal gravity, he and Trix must let their spacesuits shuffle them slowly between the ship and the airlock, while the gigantic shape of Jupiter hangs above them in the sky. By the time they arrive, Trix has a pounding headache from the vertigo. Inside the complex, she and the Doctor find that the occupants, all laboratory technicians and scientists, have been torn apart as if by wild animals. In the office of the institute’s director, Arnauld Klimt, is a body that has fallen from a great height; his features have been obliterated, but the nametag on his jacket identifies him as Klimt. While Trix examines the body, the Doctor tries to access the computer network, only to find that someone has wiped out the institute’s files with a data bomb; however, from the remaining fragments, he determines that Falsh was funding illegal weapons research, and concludes that he is now trying to eliminate the evidence.

Trix is then sucked up through a vacuum tube in the ceiling, and the Doctor follows to find her in a sterile laboratory filled with more mutilated bodies and splashes of Halcytone paint. The Doctor and Trix are then unexpectedly attacked by a chiggock, which makes a concerted attempt to kill them despite the fact that it has no brain to direct its actions. The vacuum tube is only functioning one-way, which is presumably how Klimt fell to his death, and the Doctor and Trix are thus forced to climb down the sides of the tube; the chiggock pursues them, but it also falls to its death. Having learned all they can, the Doctor and Trix return to the ship, but Trix takes Klimt’s jacket and drapes it over her helmet so she won’t have to look at Jupiter on the way back. Back on the Polar Lights, she finds a box of white pills in the jacket pocket, but the Doctor warns her that they’re not painkillers and throws the pills out, replacing them with ordinary aspirin. Trix sleeps off her headache while the Doctor sets course for the FILOC-P that Torvin mentioned, hoping to hole up there and think things through.

Fitz catches up on his sleep, and Sook wakes him and tosses iron filings onto his face; the filings come to life and chew away his stubble, leaving him with a fresh, clean shave. She notes again his unfamiliarity with this common product, but Fitz turns the tables and asks Sook about herself. She explains that her parents fled from the authorities when her mother went senile and was scheduled for termination; Sook grew up in a hostel and was taught in a backwater academy, where she learned the principles of Feng Shui. She then taught those principles to Halcyon, but Falsh’s commercialism has corrupted his artistry, and Sook has reluctantly been forced to help Gaws and Mildrid expose Halcyon for the fraud he is. Halcyon then summons Fitz to lavish praise upon him for his artistry, and agrees to intercede with Falsh on behalf of Fitz’s friends. However, it then occurs to Fitz that if the Old Preservers succeed in ruining Halcyon’s reputation, he will no longer be in a position to help -- which means that to save the Doctor and Trix, Fitz may have to betray Sook.

Falsh receives word that an unidentified ship is approaching the conference podule, transmitting his personal access codes. Falsh doesn’t want anyone to know about this meeting, and since security has been tightened following the previous incident, he leaves in his second personal shuttle, the Polar Aurora, to make contact with the approaching Agent outside. The Agent, the fish-like alien who attacked the Doctor and Trix on Thebe, accuses Falsh of treachery; the Agent’s people helped to fund the weapons research on Carme, and they believe that Falsh has stolen the product and intends to sell it to a higher bidder. Falsh offers to meet the Agent at the unfinished FILOC-P near Pasithee to discuss the situation, and the Agent accepts his terms.

Back on the conference podule, however, Tinya has taken advantage of Falsh’s absence to break into his office, and there, she finally finds what she’s been looking for all along. Satisfied, she contacts Sook to inform her that she’s arranged for tame zoo animals to be presented at Halcyon’s press conference as a gesture to celebrate the biodiversity of Old Earth. As if in passing, she also asks about the blue box that was loaded onto the Rapier. Sook notes Tinya’s interest, but covers for Fitz by claiming that it wasn’t on the ship. When she next speaks to Fitz, Sook tells him that she’s just lied for his benefit and demands answers, and the shamed Fitz agrees to give them.

Trix’s headache has passed by the time she and the Doctor reach the FILOC-P. There, they find Torvin lying in the cafeteria in a drugged stupor, and the Doctor wakes him with a white wake-up pill. The Doctor then explores the podule while Trix sits with Torvin, who has recovered almost instantly; as Fitz has already learned, drug use is perfectly legal in this century, and Torvin has a whole pharmacy of drugs that he uses to trigger specific highs and counter the side-effects of the other pills. Trix decides to turn on the television to look for word of Halcyon -- and sees a news report that changes everything...

Falsh also sees the news report, and is horrified to learn that a new life form has been found on the airless moon of Leda. Gaws Murphy claims to have been forced down on Leda by NewSystems robot drones operating in Hostile Prime mode, and to have discovered a life form like a cross between a slug and a caterpillar, living in an environment supposedly incapable of supporting life. The discovery of the “space slugs” has brought the demolition schedule to a crashing halt, as any of the moons could be capable of supporting life after all. Falsh, realising that Arnauld Klimt is to blame for this fiasco, instantly contacts the head of his R&D team, Phaedra; the slugs are being analysed by scientists from Pentagon Central, but Falsh orders Phaedra to get her hands on a sample and prove that this news is a hoax. He places Tinya in charge of PR before leaving to keep his appointment with the Agent on the FILOC-P. In the confusion, Tinya’s decision to bring zoo animals to the press op passes without comment.

Fitz has shown Sook the interior of the TARDIS and explained the truth to her. The stunned Sook then receives a frantic call from Halcyon, who is aware that he will be made to look a fool if his Grand Orchestration is cancelled at the last moment. As the Rapier touches down on Callisto, Sook tries to calm the frantic Halcyon, but realises that his reputation will be ruined forever by this stunt -- and she can’t bring herself to betray him now that she has an alternative. She thus tracks down Fitz, who is standing on the stage of the vast Medicean Stadium, gaping at the size of it. Surprisingly, Sook kisses him and then leaves, telling the confused Fitz not to hate her for what she has to do.

The Doctor has found nothing of interest on the FILOC-P, apart from the glowing Halcytone paint on the walls. Trix replays the news broadcast when he returns to the cafeteria, and the Doctor dismisses it as patent nonsense that any life form as complex as a slug could suddenly appear out of nowhere. He has programmed the podule’s computers to break the fragments of encrypted data from the research complex, but they’re taking too long and he decides to work it out for himself. Trix lends him a pencil from her borrowed jacket, and before setting to work, he notes with interest that the pencil is unbroken. He successfully deciphers the word “PAIN,” but then the Agent arrives for its meeting with Falsh, spots the two ships already docked with the FILOC-P, and destroys them both.

The Doctor rushes off to prepare for the alien’s arrival, telling Torvin and Trix to hold off the alien -- but Torvin does so by punching Trix in the head and leaving her behind as a delay while he flees in the podule’s escape pod. By the time Trix recovers, the Agent has entered the podule. It tracks down Trix and the Doctor in a room coated with Halcytone, but before it can kill them, the paint begins to glow fiercely and hypnotically. Falsh has activated the paint, and once the Doctor, Trix and the Agent are subdued, he removes his control headset; the hypnotic paint is still just a prototype, and the headset was making him queasy. He thus fails to realise that the Doctor, who has now realised that the word “PAIN” was only a fragment of the word “PAINT,” has resisted its influence and regained his senses. Trix and the Agent are now in deep hypnotic trances, wide open to suggestion, and the Doctor thus questions the Agent and learns that it has been investigating Falsh’s actions on behalf of his erstwhile allies, the Icthal. It tried to kill the Doctor and Trix because it assumed that they were rival agents seeking the ultimate weapon for themselves. Before waking Trix, the Doctor gives the Agent certain post-hypnotic suggestions...

Halcyon contacts Tinya and informs her that he will not be attending the press conference. Realising that he has a surprise planned, Tinya decides to investigate. Fitz sees her and follows her, hoping that she’ll lead him to the Doctor and Trix, but two panic-stricken chefs then run out into the corridor, claiming that they’re being attacked by a chiggock. Fitz shakes them off, but he’s lost track of Tinya -- and when he retraces his steps, he sees that chiggocks are in fact attacking the chefs and have already trampled one to death. Fitz sees a magnetic disc float out of the nearby dressing rooms and rushes in to look for help, only to discover that Sook picked his pocket when she kissed him, stole the key of the TARDIS, and has now shown its interior to Halcyon. The delighted artiste now plans to replace his failed Grand Orchestration with a demonstration of the Endless Cupboard, the new product from the inventor of Halcytone. Fitz is infuriated, but Sook insists that this is the only way to keep Halcyon happy so Fitz can be reunited with his friends. They are unaware that Tinya has been hiding nearby and has seen everything.

Falsh contacts Tinya and orders her to visit Phaedra’s R&D team; he has provided them with positive proof that the slugs are fake, and Tinya must ensure that the demolition goes ahead once their “findings” are released. Falsh then enters the FILOC-P, where he orders the Agent to believe that he has shown it positive proof of its innocence, which it will take to the other Icthal when it awakens. He then turns on the Doctor, expecting him to be hypnotised, and the Doctor promptly overpowers him and takes his gun. The Doctor then wakes Trix, and together they force Falsh back onto the Polar Aurora and leave before the Agent wakes up.

Aboard the Polar Aurora, Falsh receives bad news from Phaedra. The slugs were indeed created by Arnauld Klimt, but they still meet all the legal criteria to be classified as life forms. Also, Torvin’s escape pod is on its way to the R&D facility, and none of the researchers know who’s on board. The Doctor and Trix demand answers, and Falsh gives in and explains that Klimt misled him; instead of developing the ultimate weapon, Klimt used Falsh’s money to fund an entirely unrelated project, creating a life form that could thrive under any conditions throughout the galaxy. Klimt offered up the hypnotic paint as an offshoot of his research, but that wasn’t good enough for Falsh. He intends to cut his losses by using the nano-optic fibres in the altered Halcytone to spy on the companies that rent his FILOC-Ps, and thus acquire insider information; but he blew up the complex on Carme not to cover his theft of the ultimate weapon, but to cover the fact that there was no such weapon in the first place.

However, the Doctor isn’t so sure that this is the case. The complex’s staff were certainly killed by something, and someone presumably deleted the data from the computer net for a reason and launched the complex away from Carme in order to protect something. Also, although Arnauld Klimt supposedly died from a fall that shattered his bones, the pencil in his jacket was still intact. Perhaps the real Klimt planted his jacket on another body and is still alive somewhere. But if so, then why plant his creations on Leda? Does he just want to interfere with the demolition to embarrass Falsh, or is something else going on? And since Tinya has obviously been spying on Falsh, just who is she really working for?

Tinya is on Callisto, heading for a rendezvous with Phaedra’s R&D team, who have been given a small shed at the back of the Pentagon Central research compound. On her way, she begins to hear rumours that chiggocks are behaving oddly and violently throughout Callisto. When Tinya arrives at the shed, she orders the researchers to gather together in the central chamber -- and releases poison gas into the air, killing them all. The escape pod has touched down, and Tinya opens it up to find Torvin lying inside in a drugged stupor... except that his real name isn’t Torvin. It’s Arnauld Klimt. Tinya gives Klimt another of his white wake-up pills, and they return to the research centre to wait for Falsh’s alien bidders to contact them. As the Agent suspected, Falsh did intend to sell the weapon to the highest bidder, but now Klimt and Tinya will be the ones offering the weapon for sale. Tinya had been searching for a list of the bidders and the prices that Falsh was asking, and now that she’s found it, the auction can go ahead as planned. The Pent Cent research compound contains several slug specimens, and Leda has been blockaded in order to protect the slugs’ “natural” habitat. Soon, the demonstration of the ultimate weapon will begin...

While Halcyon holds rehearsals for the presentation of the “Endless Cupboard,” Fitz and Sook meet secretly with Gaws and Mildrid, who intend to stake a claim to the remaining moons through the Empire Trust. When Sook excuses herself from the table for a moment, Gaws and Mildrid note Fitz’s concern for her, and reveal that they’ve been blackmailing her to ensure her co-operation; she is the one who turned in her parents to the authorities. The sickened Fitz reveals to Sook that he knows what she did, and Sook, shocked and hurt by his reaction, heads to a floating control suite to supervise the broadcast. There are a million people in the arena, but the sound of their cheering is blocked by a sonic barrier, and Halcyon doesn’t acknowledge the sight of them. The TARDIS is hoisted above the stage by the robot magnetic discs, awaiting its presentation -- but just as the show is about to begin, Fitz spots Falsh standing in the wings. When he runs over to confront Falsh, he finds Trix standing behind Falsh with a gun; upon arriving, she and the Doctor split up to search for Fitz, and Trix found him first. Halcyon then appears on stage, but just as the show begins, the zoo animals from the earlier press conference batter down the door between their cages and the arena and stampede forward, aggressively tearing into the crowd, mauling and killing everyone in their path.

In the confusion, Falsh escapes, and Halcyon’s dancers also flee in terror, leaving him stuck in the middle of the stage with no idea what’s going on. The Doctor joins Fitz and Trix on the stage, and resets the arena’s force fields, causing the stadium seating to vanish and giving the audience a clear run for the exits. In the process, he accidentally deletes the stage set from beneath Halcyon’s feet, and the artiste is knocked unconscious by his fall. The Doctor then alters the sonic barrier that was blocking the crowd noise, causing it to emit a piercing whine that draws the animals’ attention. They abandon the audience and stampede towards the stage, and the Doctor then reconfigures the force fields, trapping the enraged animals between two invisible walls. Unfortunately, Sook fails to notice this, and when she tries to save the Doctor and his friends by swooping the control suite over the animals to scatter them, it crashes into the invisible wall and goes down in flames.

Fitz rushes off to help Sook while the Doctor remains on stage to stabilise the force fields. Once he’s accomplished this, he checks the local news reports, and learns of the widespread chiggock attacks; also, animals in a testing facility on Europa have also run amok. The Doctor realises the truth: the slugs are indeed the ultimate weapon that Klimt was supposed to be developing. They can survive in any environment, and somehow their mere presence inflames aggression in other forms of animal life. The chiggocks, with their rudimentary nervous systems, were the first to be affected, but the effect has now worked its way up to higher forms of life -- and soon it will begin to affect human beings. The carnage in the arena was just the beginning.

Trix is starting to get another headache, but she discovers that her aspirin are gone, and assumes that they fell out of her pocket when “Torvin” hit her. It then occurs to her to wonder how the hypnotic Halcytone could have been an offshoot of Klimt’s research, and the Doctor concludes that the paint may have some effect on the slugs. Roddle then arrives in a panic, claiming to have been attacked by a madman; time is running out, and the Doctor thus sends Trix to track down the Pent Cent labs and get one of the slugs for him to examine. Roddle, still unsure what’s going on, nevertheless agrees to pilot Trix across Callisto in his personal flying scooter, while the Doctor tends to the unconscious Halcyon’s injuries on the Polar Aurora

Fitz finds Sook in the remains of the broadcast suite; gravely injured, she confesses that the Dean of her academy threatened to expel her when she learned the truth about her parents, and they turned themselves in when she called them and begged them to do so. She has felt guilty about it ever since, which is why she couldn’t bring herself to betray Halcyon. Fitz tries to get her some medical attention, but the emergency services are swamped due to the carnage in the arena, and soldiers have erected a barricade, preventing him from getting back to the stage. He thus tries to carry Sook back to the Rapier and its medical bay, but gets lost in the service tunnels; fortunately, he runs into a cleaning robot, orders it to scrub down the hangar and follows it. Once there, however, they are attacked by a crazed mob that has fallen victim to the slugs’ influence, including Gaws. Mildrid still retains her senses, however, and when Fitz orders the drone to clean the hangar, it drenches the mob with jets of soap and water, driving them back while Fitz and Mildrid get Sook aboard the Rapier to safety.

Three alien bidders have arrived for the auction, remaining safely in their spaceships and transmitting holographic images to Phaedra’s labs. They are sceptical of Klimt’s claim to have developed the ultimate weapon, however, and when Klimt loses his temper with them, Tinya notes that he is losing his concentration and seems unable to cope with the pressure of the auction. Klimt assures her that the antidote they’ve taken will protect them from the slugs’ effect, and while the bidders retreat to consider what they’ve seen so far, Klimt takes more drugs to deal with the boredom of waiting for the next phase to begin. Meanwhile, Falsh is heading for the labs to speak with Phaedra, unaware of what’s been happening in his absence, and Trix catches sight of him and orders Roddle to follow him. They touch down near the R&D labs, but Roddle loses his temper and turns on Trix, accusing her of treating him like a fool. Before he can attack her, however, the dome over Callisto goes clear to reveal the night sky; this was the moment when the demolition was to begin. Shocked back to his senses, Roddle agrees to return to the Doctor while Trix investigates the laboratory.

Falsh uses gas capsules to knock out the Pent Cent guards when they try to stop him from entering the research complex, but Falsh and Tinya hear the commotion and capture him when he enters. Klimt reveals that he realised very early on that Falsh would have him killed once his work was complete, and thus arranged for Tinya to infiltrate Falsh’s board of directors so he’d have an inside agent. Trix then bursts into the labs and flings Halcytone paint at them, both enabling the Doctor to watch events from the control unit aboard the Polar Aurora and distracting Tinya so Trix can grab her gun. She then outlines what she and the Doctor have deduced. Klimt created the slugs to serve as the ultimate weapon, but lied to Falsh about their purpose. He launched his labs into space before Carme was destroyed in order to gain time to test the slugs on the scientists who’d helped develop them; he then faked his death and travelled to Thebe to destroy the evidence of what he’d done. However, the Icthal Agent arrived on Thebe to investigate why Falsh had ordered that Carme be destroyed, forcing Klimt to hide. The Doctor and Trix then arrived before Klimt could wipe the base’s surveillance data, and Klimt disguised himself in the real Torvin’s suit to avoid awkward questions.

Klimt, enraged, lets slip that Trix has guessed right about the effect of Halcytone paint on the slugs. However, there’s no way to get the paint to Leda, which is blockaded by Pentagon Central ships with orders to protect the space slugs. The alien bidders’ holograms then return, distracting Trix and enabling Klimt to recover the gun; however, Trix then “reveals” that the Doctor has gone to the NewSystems Demolition base to blow up Leda, and the Doctor, still listening in, realises that he has no choice but to do so. When Klimt loses his temper, the suspicious aliens sign off, concluding that this auction has been a waste of their time. The Doctor then uses the Halcytone to hypnotise the others, ordering them to obey all of Trix’s commands; however, Klimt manages to resist the Halcytone’s control and flee. Outside, Roddle has fallen victim to the slugs’ effect and is killing his way through the riot-torn streets to get back to his flyer, but Klimt gets there first, kills Roddle for the keys, and pilots the flyer back to the Rapier. Believing that the Doctor is already on his way to Leda, Klimt hijacks the Rapier and sets off in pursuit -- along with Fitz and Mildrid, who are tending to Sook’s injuries in the Rapier’s medical bay.

The Doctor sets off for Leda in the Polar Aurora, along with the protesting Halcyon. Halcyon has no idea what happened in the arena, but the Doctor reveals that he already knows the designer’s secret; when he examined Halcyon’s injuries, the Doctor discovered that he was blind. Halcyon admits that he paralysed his optic nerves while experimenting with the possibilities of Halcytone, and he’s been pushing for bigger and better things ever since to fill the void in his life. However, when Halcyon asks the Doctor insightful questions about the TARDIS’ dimensions, the Doctor realises that Halcyon is also an accomplished engineer, and insists that Halcyon help him to save the victims of Klimt’s slugs. The shaken Halcyon calms himself by giving himself a shave with his box of nanoscopic iron filings, the same type that Sook used on Fitz earlier.

Fitz investigates the hijacking of the Rapier and discovers that Klimt has murdered the pilots. Suddenly enraged, Fitz attacks Klimt and tries to kill him, even though he has no idea who the man is. In the course of the fight, however, he tries to hit Klimt with a PadPad helmet that’s still plugged in, and gives himself an electric shock. Assuming that Fitz is dead, Klimt leaves him behind when the Rapier arrives at the NewSystems base, which is located between Sinope and Callirrhoe. Mildrid and the recovering Sook follow Fitz to the bridge and find that he has regained his senses -- but only temporarily, as he suddenly attacks Mildrid and tries to throttle her. Sook saves Mildrid by placing the PadPad helmet on Fitz’s head, placing him in one of the virtual apartments he’d created from his own memories of Mechta. However, Sook herself then falls victim to the slugs’ influence and attacks Mildrid, who flees in panic -- leaving Fitz at Sook’s mercy.

The Doctor and Halcyon have arrived at the NewSystems base only to find that the staff have already killed one another. The computers have been damaged in the fighting, which means that they will have to reconnect the moons to the demolition network before they can isolate and destroy Leda. However, Klimt then docks with the base, and the Doctor is forced to leave Halcyon to do the work while he tries to hold off Klimt. They run into each other in the landing bay, where the Doctor tries to use his sonic screwdriver to drop one of the magnetic discs on Klimt’s head. He fails, and Klimt attacks him. The Doctor soon realises that Klimt took the pills from Trix on the FILOC-P, assuming, since he found them in his own jacket, that they were his wake-up pills -- and unaware that the Doctor had replaced them with ordinary aspirin. Ever since, Klimt has been using aspirin in place of the proper pills, and he’s now completely unbalanced. The Doctor has only his sonic screwdriver and Halcyon’s cloak with which to defend himself -- and as the deranged Klimt attacks him, the Doctor upends Halcyon’s shaving nanites into Klimt’s hair. He then activates the magnetic disc with his sonic screwdriver, and it attracts the nanites to itself and then rises to its default setting, out of the way up by the landing bay’s ceiling. Once the nanites have eaten away all of Klimt’s hair, he falls to his death.

Mildrid arrives, seeking help, and the Doctor learns from her that Fitz recovered his senses after a shock to his system. He and Mildrid return to the base’s control suite, where they find that one of the base’s staff survived the slaughter after all and is now attacking Halcyon. Mildrid rescues Halcyon, but he then goes mad and attacks her; however, he snaps out of it when the Doctor points out that he can see again, presumably as a result of the slugs’ psychic assault on his nervous system. Halcyon confirms that he’s linked all of the moons into the network, but that he didn’t have time to isolate Leda -- and before Mildrid can stop him, the Doctor orders the computer to detonate all of the moons at once.

Back on Callisto, Trix learns that Klimt provided Falsh with an immunity to Halcytone’s hypnotic effects; however, since Falsh has no protection against the slugs’ effects, he agrees to a truce until they have been destroyed. He and Trix track down the slugs in the main laboratory complex, where the scientists who had been testing them have now killed each other. Trix destroys the slugs by coating them with Halcytone, but Falsh spots a sealed centrifuge elsewhere in the room, and Trix is forced to climb up into the rafters to get a look inside. The centrifuge is empty, and Falsh thus declares the truce over and shoots at Trix, forcing her to drop into the centrifuge. Falsh tosses a grenade in with her, and although Trix promptly tosses it back out again, the explosion sets fire to the laboratory. Fortunately, a burning rafter falls into the centrifuge, enabling Trix to climb out. By this time, however, Tinya has shaken off the Halcytone’s influence, and she forces Trix back to the stadium at gunpoint, intending to flee in the TARDIS. On the way back to the stadium, however, the Jovian moons explode, a fantastic and terrifying display of fireworks that shocks everyone who sees it back to their senses. In the ensuing confusion, Trix flees back to the stadium, and when Tinya arrives, Trix drops the floating TARDIS on her; she misses, but only by millimetres, and manages to grab the gun from the surprised Tinya.