An explosion that tears the sky apart. A man whispering: “...beautiful.” A woman telling the Doctor of her long and fruitless search for a cure, and how her wish to experiment in zero-gravity environments led to her purchasing a space station where the Koteem contacted her in secret. The sounds of screams and sirens and slashing as Nyssa struggles with another young woman for a knife...

Later, on a long journey and still four days from their destination, Nyssa asks the Doctor if they really should be working with Quain and his people. The Doctor admits that he isn’t sure; there are a lot of deeply held convictions on this planet, and it’s difficult to tell who’s right and who’s wrong. All he does know is that it’s not only the Veln and the Koteem whose survival is at stake. The sooner they get to the TARDIS and leave, the better.

The Veln security block’s chief psychiatric interrogator, Brodlik, arrives in his superior Gilbrook’s office with tapes of the recent interrogation. The security minister is demanding answers, and Gilbrook thus gets straight to the business at hand rather than taking the time to make Brodlik squirm. For the record, this interview is about the recent alien incursion by the Koteem, or so Gilbrook claims. Brodlik isn’t so sure that this is what happened. But it can’t be denied that the prisoner is a beauty -- apart from the bruising caused during her arrest.

Brodlik’s interview with the prisoner begins with a correction; the records give her name as Nyssa Traken, but she explains that it’s really Nyssa of Traken. Though released from hospital, she remains shaken by what she’s gone through; nevertheless, she’s startled to learn that Brodlik is here to assess her psychiatric state. Brodlik claims that she made certain bizarre statements at the time of her arrest, but she points out that she was suffering from concussion after her beating. All she wants is to return to her friend, the Doctor.

Reviewing this part of the interview, Gilbrook points out that they could have saved a lot of trouble if Brodlik had had his prisoner describe her friend so they could pick him up. At this point in the interview, Brodlik was interrupted by the arrival of Nyssa’s medical reports -- but though Brodlik claims that the rest of the interview isn’t significant, Gilbrook insists that he play it back anyway.

On the tape, Brodlik returns to the interview room and reveals that blood tests confirm that Nyssa is alien to Veln. She is surprised by his acceptance of this fact, and by how bitter his attitude has suddenly become. She has no idea what he means when he speaks of her people’s legacy, or so she claims; he’s certain that she is a Koteem, and doesn’t believe that she’s ignorant of what happened on this world. He forces her to look at his face -- his hideous face, bent out of shape by scar tissue and warped bone structure. Since Nyssa was found on the Lady Forleon’s estate, she must know that only the rich and powerful can afford the cosmetic surgery to make themselves look as the Veln once did before the Koteem poisoned their world. Nyssa has some idea of what he means by this, though she still claims to be unaware that the dyestrial toxins in the atmosphere were the result of alien interference. She’s appalled when Brodlik reveals that the security forces have “dealt with” a number of Koteem agents in the past, and tries desperately to convince him that, although alien, she’s not a Koteem. As a psychiatrist he must know that she’s not lying to him. Her blood was compared against Veln samples -- but was it compared to other Koteem samples?

It’s at this point that Brodlik made his great mistake. He should have turned the Koteem agent over to security immediately, but her behaviour at the interview had rattled him. Gilbrook demands to know exactly what happened next, and when Brodlik hesitates, the impatient Gilbrook finally makes it clear just how much trouble Brodlik is in. Instead of following procedure, he went home three hours early, breaking every security regulation on the books. And Gilbrook needs to know what happened next.

When Brodlik arrives at home he is confronted by two men in pollution masks who force their way into his apartment -- and remove their masks to reveal that they aren’t as horribly mutated as the third-generation Brodlik. Brodlik, disgusted by what their beauty represents, assumes that they are both Koteem agents. The one man insists that he’s no such thing, and that he only wants to rescue his friend Nyssa, leading Brodlik to realise that this must be the “Doctor” she spoke of. Though furious to learn that Nyssa has been beaten by the arresting officers, the Doctor nevertheless appears disturbed when his associate Quain begins to put the pressure on Brodlik; however, he wants to rescue Nyssa, and he has little choice but to let Quain do his work. Quain reminds Brodlik of the terrible things that happen in the security block -- and warns him that if he doesn’t help, similar terrible things will happen to his family.

Of course, Brodlik doesn’t tell Gilbrook any of this later, and claims that he simply went home to think over Nyssa’s claims. But he’s lying, and Gilbrook has video evidence that Brodlik in fact came back that night and entered the medical department. Brodlik admits that he returned to compare Nyssa’s blood samples to those from known Koteem agents, and found that they weren’t even remotely similar. As far as Gilbrook’s concerned this just means she’s a Koteem with a different blood type, and in any case Brodlik didn’t bring it up with the medical examiner as he claims he’d intended to do. Gilbrook orders Brodlik to play the next tape, but it cuts off almost as soon as it begins, apparently due to a fault in the system -- a fault with curiously coincidental timing, as it was at this point that the intruders entered the building. Brodlik claims that their documents were all in order and that he had no choice but to hand over his prisoner to them. Gilbrook patiently asks one question: what really happened?

Once Nyssa and Brodlik are alone in the interview room, Brodlik operates a device provided by the Doctor and Quain, jamming the surveillance systems. He’s ashamed of himself for giving in to them, and he’s angry and disgusted with Nyssa, who will get away scot-free with what she’s done. Nyssa insists that she’s innocent, but Brodlik has met her violent friends and he knows better. He just wants to know one thing: isn’t it enough that her people doomed his world to a slow and terrible death? Why did she have to come back to murder and mutilate one of the Veln?

There are sirens and screams, and, as Nyssa struggles with another young woman for a knife, the terrible sound of slashing.

The Doctor hears screaming from the direction in which he left Nyssa, but as he turns back to investigate he is accosted by two men with guns, Seedleson and Murone. Lady Forleon’s orders regarding secrecy are very clear, and they won’t hesitate to shoot if they have to. As the screams die away and sirens begin to wail, Seedleson and Murone escort the Doctor to the house and send out another patrol to pick up his landing pod before it’s discovered.

Lady Forleon is trying to deal with the fiasco, no doubt caused by a local hearing the screams and calling the security block. Oddly, it seems that another girl has been arrested, but the report Lady Forleon is hearing makes no sense to her. Quain then reports that the replacement has arrived ahead of schedule -- and in broad daylight, no less -- but that he seems confused and disoriented. Forleon invites the new arrival, “Doctor”, in to speak with her, but soon realises what Quain means; the Doctor seems to believe that he’s a prisoner and claims to have known the screaming girl, which makes no sense if he’s only just arrived. The Doctor explains that he’s here because of the dyestrial toxins in the atmosphere, which Forleon already knew, but when he claims to have approached the house to warn its inhabitants about the dangerous of dyestrial fallout, Forleon concludes that he must be suffering from concussion or brain damage caused by a bumpy landing.

Quain then arrives to inform Forleon that they’ve found the Doctor’s landing pod, and it’s like nothing they’ve ever seen before. The Doctor accompanies them to the building where the pod, his “TARDIS,” is being readied for transportation, and admits that he’s from another planet. He is surprised by Forleon and Quain’s own lack of surprise, but gives up trying to understand for the moment and returns to the subject of Nyssa. Forleon finally realises that the girl he mentioned isn’t Veline at all, but the other girl described in her guards’ report. Murone then arrives with a surveillance photo of the beauty who was arrested for murdering Veline, and the Doctor is appalled to see Nyssa, with blood on her hands, being bustled away by uniformed security men, and finally demands to know exactly what’s going on here. Forleon realises that the Doctor genuinely doesn’t know, and orders Murone to cover him with his gun. Suddenly the Doctor’s lack of knowledge has become very worrying indeed.

Later: Nyssa is free, but the Doctor doesn’t believe that Quain helped out of the goodness of his heart. He said he’d drive them to the TARDIS, but now, after several days’ journey, their transport has stopped in the middle of a snowy wilderness which reminds Nyssa of {Alaska}. Quain is aware that the Doctor doesn’t trust him, but assures him that what they’re doing here is for the benefit of all Veln -- even if the Veln don’t actually believe that. They have stopped in front of what appears to be a hill but is actually a holographic projection created by Koteem technology, which Veln security forces can’t hope to understand, let alone penetrate. Quain lowers the force field to let the Doctor and Nyssa inside the Koteem ship, but they are subjected to a bioscan and realise that they’re to be interrogated by a Koteem. Nevertheless, the TARDIS is being held somewhere in this base, and if they ever want to leave this planet they’ll have to co-operate. The Doctor and Nyssa thus speak with a Koteem who prefers not to give its name. It shouldn’t be here at all, and before it releases the Doctor or Nyssa it must know whether they intend to inform the Galactic Sector Council of its presence.

The Doctor assures the Koteem that he barely understands what’s happening on Veln and has no intention of interfering. But how can the Koteem be sure the Doctor is telling the truth? It asks the Doctor for his personal opinion about what’s happening here. Having seen a Koteem in person, the Doctor believes that it is also suffering from the effects of dyestrial pollution, which implies that its people’s fate is linked with that of the Veln. The Koteem explains that his people chose to use dyestrial as their primary energy source, but realised too late the devastating ecological and genetic side-effects this toxin caused. The Galactic Sector Council gave them permission to dispose of the toxic waste in an uninhabited sector of the galaxy, but avoiding the Veln solar system added time and costs to the operation, and the company in charge of waste disposal found it more profitable to take the occasional short cut. Four generations ago, there was an accident; a transport ship broke up in orbit around Veln, and the planet was terminally polluted. In another four generations, the Koteem will be guilty of genocide. But this particular Koteem and his associates have a plan to prevent that...

Gilbrook has obtained a search warrant for the Forleon estate, and he’s enjoying watching her squirm as his men tromp through her lovely home, despoiling its beauty. He’s had to look at filth and ugliness all his life thanks to the Koteem, and it seems normal to him now; it’s the beauties, the ones who take advantage of governmental corruption to bribe their own way out of danger while using cosmetic surgery to “elevate” themselves above the ordinary Veln, whom he finds ugly. He finds the arrogant Forleon particularly sickening, and he’s determined to prove that she’s been harbouring Koteem agents -- and when he does, all of her government contacts will desert her, and she’ll end up behind bars, where she won’t stay beautiful for long.

Despite Forleon’s attempts to soothe Veline, the intramission procedure goes horribly wrong. Before Quain or Forleon can stop her, Veline shrieks in agony, tears free of her restraints and breaks out of the basement, taking a scalpel with her. Seedleson and Murone detect the break-out and contact Forleon, who orders them to make sure that Veline is restrained but unharmed. Quain admits that the last time something like this happened, the patient died inside, but this time there are wider concerns. If Veline gets out of the grounds the consequences could be disastrous, and just to complicate matters, the perimeter scanners have detected something the guards can’t explain. Forleon sends Seedleson and Murone out to investigate, but she’s already too late; the security block is now aware that something odd is happening on the estate, giving Gilbrook just the excuse he’s been waiting for to enter the estate.

Veline manages to get past the gate guards, and while looking for her, Seedleson and Murone find someone else -- a blond figure in weird clothes who doesn’t look ugly and must therefore be a Koteem. Murone suggests shooting him as payback for what his people did, and claiming that he panicked and made a run for it. Seedleson works for Forleon because he believes in what she’s trying to do, but Murone doesn’t trust her or the Koteem and only works here because the pay is better than in the security block. Disgusted, Seedleson sets off to capture the newcomer. Meanwhile, Veline encounters Nyssa, who tries to talk down the distraught woman to no avail. Veline can feel something in her head, suffocating her sense of self, and she begins to hack at herself with the knife. Nyssa struggles with Veline as she slashes away at herself, screaming, and sirens approach from outside the estate...

Nyssa is taken into custody for Veline’s murder, but insists that she was trying to save the woman, who was slashing away at herself as if trying to cut something out from inside her. Her story is weird enough for Gilbrook to hand her over to his chief psychiatric interrogator, Brodlik; he doesn’t particularly care that a beauty was murdered, but this case could give him the opportunity to raid Forleon’s estate and wipe the perfect, beautiful smile off her face, and he wants to be sure that everything is in order. Nyssa has spoken of alien things, which means that she must be a Koteem; the medical team claims that there’s something odd about her blood samples, but Gilbrook dismisses their confusion as incompetence on the technicians’ part and ordered them to run the tests again. In the meantime, Brodlik is in charge.

On the Forleon estate, the Doctor has been questioned by Forleon and found wanting, and is now being held at gunpoint by Murone. Either he’s mentally ill or an impostor from the security block; in any case, his presence threatens the entire project. He is forced into the operating theatre and given a level-one bioscan, which produced truly strange results implying that he is neither a Veln nor a Koteem. Disoriented by the scan, the Doctor tries to recall who these “Koteem” are and causes some consternation by referring to them as an extinct species, which must not be the case yet. But the Koteem are an arthropod race, entirely unlike the humanoid Veln, so why were Quain and Forleon initially under the impression that the Doctor was one? And since Nyssa obviously isn’t responsible, who did kill Veline? Forleon admits that Veline killed herself, but that security chief Gilbrook, will have seized the opportunity to arrest Nyssa and put a beauty on trial for murder. Forleon realises from the Doctor’s reaction that he truly knows nothing about the state of affairs on this planet -- but while he seems harmless enough, she decides to withhold judgement on him for the moment.

Later: Quain has helped to rescue the Doctor and Nyssa, and takes them to the Koteem along with a shipment of travel pods which will be reused to send more simulacra down to Veln. The Doctor still isn’t sure whether to approve of what’s happening here -- it’s almost like an invasion -- but neither species seems to have much choice. To Nyssa’s surprise, after their interrogation, the Koteem has decided to let them go, and the Doctor has decided to take the opportunity, as the situation is too complex for him to judge. His intentions were good, as were Nyssa’s, and sometimes that’s all one can hope for. Perhaps Nyssa’s arrest led to the raid on the Forleon estate, but Veline would always have killed herself, and the security people would always have had that as an excuse. Quain and the Doctor no doubt stirred them up when they rescued Nyssa from the security block; despite Brodlik’s unwilling assistance and their forged documents, their departure aroused suspicion and they were lucky to escape with their lives. However, the Doctor feels that they were simply swept up in events. The Veln were trying to protect their people from what they saw as an alien threat, and the Koteem were trying to make amends for their terrible mistake -- and the Doctor and Nyssa probably had no influence over anything.

But the Doctor is unaware of what took place after Nyssa’s escape. Despite the circumstantial evidence of wrongdoing on the Forleon estate, Gilbrook is unable to get authority for a search warrant -- and he thus turns to Brodlik, demanding the truth about the men who rescued Nyssa and why the surveillance cut off so conveniently. When Brodlik hesitates, Gilbrook begins to beat him brutally. Whatever the intruders threatened to do to Brodlik’s family, Gilbrook will do that and more besides, unless Brodlik confesses the truth and gives Gilbrook the evidence he needs to mount a raid on the Forleon estate.

A Koteem waste transport ship has entered the Veln system illegally. To avoid detection by the galactic authorities, they must run silent, and when alarms sound, indicating a leak in the aft section’s toxin containment fields, the captain orders the pilot to shut the fields off until they’ve cleared the system and it’s safe to advertise their presence again.

The Doctor and Nyssa have been conducting repairs to the TARDIS, which has drifted into the Veln system while they’ve worked. According to the TARDIS data banks, the Veln are currently on the brink of developing interplanetary space travel, and other species are forbidden from entering the system during this culturally delicate time. The Doctor decides to materialise briefly to test the newly-repaired power relays, but the helmic regulator slips, causing them to drift into Veln orbit -- and an alarm indicates the presence of dyestrial toxins in the atmosphere. The Doctor attempts to dematerialise, but the dyestrial interferes with the power relays, and the console shorts out, causing the TARDIS to lurch as though it’s hit something. The TARDIS leaps forward about a century or so and then materialises again, forced to touch down while it conducts self-repairs on the damaged power relays.

The planet’s atmosphere is still contaminated, but it’s safe to breathe for short periods; only extended exposure to the toxins is dangerous. The Doctor emerges for a look around, and he and Nyssa are pleased by the beautiful gardens surrounding them. Fascinated by the manor house in the distance, the Doctor decides to take a closer look; such beautiful architecture must be the product of a civilised mind, and perhaps the Doctor can deliver a warning about the dangers of using dyestrial as an energy source. Nyssa remains by the TARDIS to keep an eye on it, but soon after the Doctor departs, she hears a girl screaming.

Nyssa is subsequently arrested for Veline’s murder. As far as Gilbrook is concerned this is an open and shut case. He’s only interested in using it as an excuse to raid the Forleon estate, and doesn’t listen to his medical officer’s report, which suggests that the killer was trying to dig something out of the victim’s body.

Meanwhile, the Doctor is captured, analysed and questioned by Quain and Forleon, and Forleon contacts the Koteem to warn them that another alien, neither Veln nor Koteem, has stumbled across their operation. He seems ignorant of what they’re doing, but Forleon’s Koteem contact decides to question him in person. The Koteem also advises Forleon to rescue the Doctor’s friend before she tells security anything which could compromise the operation. Forleon thus speaks to the Doctor, who explains that he and his friend had no intention of getting involved and just want to leave peacefully. He left his ship and approached the manor house out of curiosity and good intentions, but that was clearly a mistake on his part -- and now Nyssa is in danger of being executed for a murder she didn’t commit.

The Doctor begs Forleon and Quain to help him rescue Nyssa, and Forleon agrees to do so. The Doctor realises that she has her own reasons for doing so, and his curiosity gets the better of him again. From what little information he’s gathered he deduces that the Koteem are sending the Veln something they need, but what? Forleon is offended by the Doctor’s attitude; he seems to be treating the life and death of her world as an intellectual puzzle. She brutally informs him that, outside this estate, Veln is all but dead; dyestrial pollution has resulted in the destruction of food crops, the slow mutation of the people, and a global economic and social meltdown. Forleon’s mother tried to block out the outside world by creating a paradise of her own, but Forleon herself has spent all her fortune searching for a cure for the genetic illness ravaging her people. It was a long and fruitless search, until her wish to experiment in zero-gravity environments led to her purchasing a space station where the Koteem contacted her in secret and offered to provide her with their own genetic essence...

Later: Nyssa has been rescued, and she and the Doctor have been transported to a Koteem base for interrogation by Quain’s alien associate. The Koteem have discovered how to transfer their essence, but the essence doesn’t survive for long in artificially constructed bodies. But when the essence is transferred into the body of a Veln, it undoes the genetic damage caused by the dyestrial pollution. Very little of the Koteem essence survives the merging, but these Koteem have accepted their fate and wish only to make amends by giving their lives to save the Veln. Unfortunately, the accident has made the Veln bitter and paranoid, and they have rejected all of the Koteem’s attempts to make restitution -- and the Galactic Sector Council has outlawed all contact with the already paranoid Veln. Thus, what these Koteem are doing here is illegal. The Doctor isn’t sure whether to approve, but concedes that all of the Koteem and Veln involved in the operation are volunteers, that Veline’s death was a tragic accident, and that the Veln security forces’ prejudice has blinded them to the benefits of co-operating with the Koteem to find a solution. The Doctor and Nyssa promise to remain silent, and the Koteem decides to let them go. Quain isn’t sure that this is wise, but concedes that he too had to make a difficult decision regarding trust when the Koteem first contacted him and Forleon.

Gilbrook’s men have torn apart Forleon’s estate, but she, Quain and the Koteem have escaped to resume their operation elsewhere on the planet. Gilbrook has found the location of the Koteem base in Forleon’s files, but it’s several days’ journey away, and by the time he, Brodlik and the security forces get there, there’s no sign of the Koteem anywhere. Gilbrook is back at square one, but he won’t let this setback stop him; he won’t rest until every one of the Koteem has left his planet alone. Gilbrook’s great-grandfather was in the fields when the Koteem ship exploded, and his story has been passed down from generation to generation -- of vast fields full of food that could feed thousands, and of the light spilling across the sky and the filthy alien poisons bringing their world to an end. According to Gilbrook’s great-grandfather, at the time it seemed almost... “...beautiful.”

To avoid detection by galactic authorities, the Koteem waste transport ship is running silent through the Veln system. They don’t expect to encounter any other spaceships, but as they pass by the planet an object unexpectedly materialises before them -- a cuboid object which, though stationary, is emitting a warp distortion field. The pilot tries to alter course, and the object dematerialises as mysteriously as it appeared -- but toxin containers have been smashed in the aft section, where the captain had earlier ordered the containment fields shut down. The ship breaks up, and lethal amounts of dyestrial toxins are released into Veln’s atmosphere, polluting the planet and dooming its people to a slow death. And four generations later, the Doctor and Nyssa depart from the planet, believing they’ve had no influence on events -- and unaware that the TARDIS had a far more devastating impact than they could have imagined...