Dramos, a satellite of the gas giant Titania, is one of the most distant outposts of the Earth Empire, but it has been abandoned following the fall of the Overcities. Humans and non-humans mix together freely in the overcrowded Habitat, which is policed by the Church of Adjudication. Control has been established via the computer network OBERON, which has been installed with limiters to ensure that it doesn't spontaneously evolve into an artificial intelligence. Dramos is currently experiencing the "crazy season", a period when a swirling red storm known as the Node appears on Titania and people in the Habitat become somewhat more violent than the norm. This year, the crazy season is even worse, and the Adjudicators, including the dedicated Joseph Craator, are pushed to their limits. What they don't yet realize is that in the slums and crevices of the Habitat, people's bodies are altering as well, becoming something other than human...

The Doctor visits the Habitat to investigate a blank area in the TARDIS data banks, which suggests that he was involved in this period in its history. Peri begins to suffer from culture shock upon seeing so many different alien types in one crowded, small area, but the Doctor snaps her out of it with a particularly thoughtless and hurtful comment. Furious, Peri storms off to explore by herself, just as the Doctor had intended; however, he suddenly realizes just what he's done to her. Subconsciously he still blames her for his previous self's death, and he's been trying to distance himself from her while telling himself he's working towards a greater good. He sets off to make amends, but on the way he must step in to save a centipedal alien from bullying humans. The alien, Queegvogel Duck Duck Duck Duck Duck Duck Seven, thanks him for his help, but both then notice a large number of Adjudicators entering the area, prepared to do battle.

Peri gravitates towards an area where a number of humans are assembling, and learns that they are holding a public rally for Human First, an organisation opposed to the cruelty of the Adjudicators. Despite the cynical comments of a bystander named Kane, Peri is impressed by their bravery in holding the illegal rally, and their leader Avron Jelks' determination to speak his mind in public. When a shock team of Adjudicators storms the rally and begins to violently "subdue" the attendees, Peri and Kane join a group of people who seem to have predicted this and prepared a way out. This is White Fire, the inner circle of the organisation, and when Kane saves their lives from the attacking Adjudicators the officer Draker welcomes him and Peri into the group. Peri, however, knows that Kane is just playing along to save his own skin, and intends to denounce him at the first opportunity.

High Churchman Garon has ordered the Adjudicators to use "Minimum Necessary Force", a euphemism for extreme prejudice; nevertheless, just as Garon had predicted, Craator disobeys the order and uses a nerve gas to incapacitate the crowd without killing them. The Doctor and Queegvogel are caught on the outskirts of the riot, and the gas has an adverse effect on the Doctor's inhuman physiology and nearly kills him. He shuts himself down completely while he recovers, but in the meantime his body is sent to the recycling centre and is found not be human. Before the Adjudicators can conduct an autopsy he recovers and awakens. Garon goes momentarily mad, accusing him of mocking the sanctity of Holy Resurrection, but he snaps back to normal within seconds. Craator tries to interrogate the Doctor, but realizes that his prisoner is trying to annoy him deliberately to keep him off balance, and has him thrown into the Holding Cells with the other aliens.

White Fire has made their base in the ruined Mimseydome, all that remains of a theme park which was built to draw tourists to Dramos before civilisation collapsed. There, Kane gets Peri alone and threatens to kill her if she tries to turn White Fire against him. Shocked and disoriented, she gets to her assigned quarters and falls into a deep sleep, and the next day, she and Kane are both enlisted into White Fire's army and given weapons training. Peri is starting to get a handle on the situation; White Fire is in fact a well-trained paramilitary organisation planning to seize control of the Habitat from the Adjudicators. Peri fully agrees with their hatred of the Adjudicators, especially after the violence at the rally; nevertheless, Draker suspects that she may be a weak link, and decides to keep an eye on her. Peri is thus assigned to Draker's squad, along with Kane, as White Fire prepares to make its move.

The Doctor is reunited with Queegvogel in the Holding Complex, a cavernous facility in the depths of the Temple of the Church of Adjudication. There, human and non-human prisoners are mingled together with little consideration given to the inevitably resulting tensions. The Doctor notes that most of the prisoners have already formed their own cliques, and senses that someone is trying to increase the tension even further. Before he can investigate, several prisoners, including the Doctor and Queegvogel, are selected by a group of Adjudicators known as the Hands of God, who answer only to Garon; they are to be taken to meet God. All throughout the Habitat, people are mutating into fleshy, glowing lumps of protoplasm, and are following a call which seems to originate from the OBERON systems in the heart of the Temple.

Craator, having calmed down, intends to resume the Doctor's interrogation, only to be told that the case has been reassigned. While returning to the Temple to investigate, he discovers that a group of prisoners he arrested earlier for a misdemeanour have been brutally executed in public. Shocked, he contacts Nadia Chong, an operator in Adjudicator control who has been under observation for hacking into the computer systems to assign a power upgrade to her apartment. Chong reluctantly hacks back into the computers to investigate Garon's activities, and discovers discrepancies amongst the Holding Complex records. There are more people going in than coming out, and there is no indication of where the missing prisoners have gone.

Prisoners from White Fire instigate a riot within the Holding Complex, and when Adjudicators are called in from the Habitat to deal with the riots, the White Fire troops outside make their move. As the Habitat descends into open warfare, Draker's group seizes control of a hydroponics facility, and to test Peri's loyalty to the cause, Draker orders her to kill the aliens who were operating it in cold blood. Peri finally realizes what kind of organisation she's joined, and Kane, upon seeing her refusal to slaughter the Darbokians, reveals himself to be an undercover Covert Ops Adjudicator and breaks cover to prevent Draker from killing Peri. He takes Peri to a flyer with which they can return to the Temple, and, realizing that she genuinely had no idea what she was getting involved in, confirms her dawning realization that White Fire is a human supremacist movement and that Avron Jelks is a madman devoted to the extermination of all non-human life forms.

The select prisoners are brought to the OBERON system, where they see that a seething mass of protoplasm is surrounding the computers. Garon worships it as God and has been sacrificing prisoners to it for some time now, and he prepares to do the same to this latest group. Craator leads a team into the OBERON levels to demand answers, but the Hands of God seize Craator and his men, who are unable until it's too late to respond to the fact that their attackers are fellow Adjudicators. The Doctor realizes that Garon knows on some subconscious level that the creature he worships isn't really God, and that the conflict has driven him mad. Before the Hands of God can sacrifice their prisoners, however, White Fire attacks the Temple and breaches the OBERON level, bringing Avron Jelks to meet his God.

Peri and Kane arrive in the midst of the fighting, and when Peri sees Avron Jelks she nearly kills him in response to what he made her see in herself. The Doctor, however, stops the fighting with a single shout, demanding that the participants look at themselves and see what they've become; Garon and Jelks have turned to an external force to fill the void within themselves, and the others have submitted themselves to become the servants or victims of madmen. The only people who have actually tried to make things better, such as Kane, have been ignored or treated with contempt, and points out that Kane, whose lover Nadia Chong has been killed during the fighting, has now gone nearly mad with grief. Jelks and Garon, both believing they are the spokesmen of God, try to commune with the energy being but are killed when they come into contact with it. The Doctor attempts to communicate with it himself, and is nearly killed in the process, but Kane snaps out of his catatonia and shoots at the creature. He hits the AI-limiters which were preventing OBERON from achieving sentience, destroying them, and the creature immediately transfers itself into OBERON's systems, which was its intention all along. In doing so, it restores all of the beings which it had transformed to give itself a new body.

The Doctor explains that the creature was in fact an extension of the Node, a living organism which was being poisoned by effluvia from the Habitat; the "crazy season" was caused by its attempts to communicate. The Node has now vanished from Titania forever, and OBERON seals itself off, unwilling or unable to speak with the occupants of the Habitat. With the death of Garon, Craator becomes the acting Adjudicator-in-Command, and he begins to enlist non-human Adjudicators to fill up the ranks and restore order. Even Benny Kane is beginning to recover, although he's surprised that the Doctor he's met is nothing at all like the family legends claim. The Doctor and Peri depart, knowing that the Habitat will still suffer from the food riots and other horrors depicted in its history, but hoping that their influence has ensured things won't be quite as bad as they could have been.