While enjoying some downtime on Red Dwarf, the posse pick up the ident signal from a nearby space station. Along the way, Kryten reveals that the lunar space station in question is a scientific research station owned by United America; an Earth coalition which came into existence after they prevented global war. By annihilating any who refused to sign their peace accord.
The station's purpose: to use the power of science to genetically cure evil. Upon arrival, they realise just who had been interred at the station. Josef Stalin, Adolf Hitler, Vlad the Impaler and Messalina; Roman Emperor Claudius' murderous and nymphomanic third wife. Overseeing the cured former evildoers is Professor Shaul Telford, a wheelchair-bound researcher who quickly reassures the Dwarfers that there is nothing to fear before inviting them for lunch.
Sure enough, the dinner table is set and already graced with the presence of the aforementioned patients, whose far-from-evil demeanour comes across as rather unsettling. After reluctantly enjoying some food, the Dwarfers go their separate ways in order to find spare parts to repair Starbug's main thrusters.
Hitler pays Lister a visit, while Messalina does the same with Cat. While Cat quickly brushes her aside, thinking the glass of milk to be poisoned, Lister soon finds himself rocking out - surprisingly now able to actually play! - with Hitler. However, when the Dwarfers return to Starbug, they discover problems.
Kryten informs them that a nearby proto-planet's orbit has it on a collision course with the moon on which the research station is situated and, in less than ten hours, the entire complex - and all inhabiting it at the time - would be destroyed. For a moment, the Dwarfers find themselves in a moral dilemma. By leaving the moon once the sandstorm has passed, they would in fact be committing an act of selfish evil, much like the ones which the patients had once done.
However, before they can reach a final decision regarding what to do, the posse are rendered unconscious one by one; Cat and Lister from having been previously drugged, Kryten from having his hard drive shut down through hacking and Rimmer by having his light bee remotely deactivated.
When they all awaken, they each find themselves in a torture scenario eerily reminiscent of the patients of the research station. Kryten has been decapitated and his (still operational) head impaled on a spike, Cat is locked in a gradually-filling water tank, Lister is strapped to a medical bed and is about to be subjected to castration and Rimmer is sealed inside a coffin and, as far as he knows, buried alive.
It doesn't take long for Lister to free himself and, after doing so, round up the rest of the team. After extricating Rimmer - who in fact had been sealed in a waste disposal pod - they immediately go to confront those they think are responsible: the "Evils". However, despite the manner of their respective predicaments and how Rimmer was sealed with Hitler's lighter, the evil quartet deny everything.
Kryten then suggests an alternative: use the station's computer system to subject everyone to a psycopathy scan. By doing so, they find out who on the ship hasn't been cured of their evil. In a sudden twist, the scan reveals the presence of two psychopaths. The first is Cat, due to his feline nature and almost overwhelming narcissistic vanity.
The second is Shaul Telford himself, who reveals that the evildoers - initially thought to be genetic clones of the historical figures - were in fact reprogrammed android scientists and that he was the research station's only patient; remanded there after having started United America's "War Against War" by brainwashing Earth's population country-by-country and turning them on one another.
Telford tries to turn Cat over to his side, citing that housecats - of whom Cat is a genetic descendant - have no actual loyalty to anyone save themselves. Cat eventually agrees to join up with Telford on the condition that he be the one to shoot the rest of the Dwarfers. Telford allows the request and hands him a blaster pistol... which Cat summarily uses to shoot the psychotic doctor in the head and save the day.
"Cured" contains examples of:
- Adolf Hitlarious: Who really enjoys a guitar-jamming session, though he is prone to giving accidental Nazi salutes.
- The Alleged Car: Starbug. In order to jumpstart it, the crew need to activate several switches and levers. Not to mention its right thruster is broken, meaning it can only make left turns.
- Buried Alive: After getting disabled, Rimmer wakes up inside a coffin, his worst fear. Then it gets worse when the thing is set on fire.
- Chekhov's Gun: The above-mentioned complex multi-person procedure needed to get Starbug started; because of it, Telford is unable to steal the ship and escape.
- Chekhov's Skill: Erecting a convincing poker face. At the start of the episode, Cat is utterly useless at it but, by the time the episode ends, he flawlessly pulls one off to save the day. Even if he can't remember what the technique's actually called.Cat: How's that for a pokey face, huh?
Lister: It's poker face!
Cat: I only have to know how to do it, not say it!
- Detect Evil: To find out who tried to kill them, the Dwarfers use a scanner in the lab room that can detect psychopathic personalities. It turns out that both the Cat and the Professor fit the bill.
- Evil All Along: The seemingly benevolent Professor was actually a patient of the facility, while the evil historical figures are actually androids.
- Genetic Memory: The crew briefly discuss this, with Kryten pointing out how Primal Fears (such as a fear of rats) can be passed down from one's ancestors.
- Hypocrite: United America. They believed in ending all war, but would go to war with anyone who didn't join them.
- Murder by Cremation: Rimmer is about to be incinerated inside a waste disposal unit before the rest of the guys rescue him.
- Ninja Prop: The actors playing the villains don't really look much like the real historical figures, most notable with Adolf Hitler who has the most screen time. The audience is just accepting this as Ability over Appearance casting - until it turns out be a plot point.
- Reality Ensues: Even if the Cat is, by human standards, a psychopath, that doesn't mean he has any incentive to kill the Dwarfers for Professor Telford. He may not like Rimmer, but he does like Lister and Kyrten... more importantly, they're his crewmembers; he doesn't want to lose his stuff. Also, Telford tried to torture and kill the Cat earlier, and whilst Cat may not be the brightest fish in the bucket, he's not that stupid.
- Robotic Reveal: The historical villains turn out to be androids modeled on the four scientists who tried to cure the actual psychopath — the professor.
- Skewed Priorities:
- When Cat finds himself in a room filling up with water, he cries out in horror... because his suit is dry-clean only.
- When Kryten learns that his head has been removed from his body and placed on a stick, he frets that the lack of arms means he won't be able to mop ever again.
- After the computer provides a list of flaws that denote Cat as being a psychopath, he's outraged - because it left out "handsome".
- Take That!:
- Kryten points out that most psychopaths don't end up becoming killers, and that most become bankers, CEOs and politicians.
- One of the station's patients is stated as being Rupert Murdoch, who is apparently "not responding to treatment".
- Tempting Fate: When Rimmer finds himself trapped in a coffin, he tries to calm himself by claiming it can't get any worse. Then he learns he's about to be incinerated.
- The Unsmile: Hitler has a constant smile that is far too creepy to make him amiable.
- Your Worst Nightmare: The Dwarfers are knocked unconscious and exposed to their worst fears: