Bats in the Caves of the desert planet Androzani Minor produce Spectrox. Citizens of populated Androzani Major require the drug for its life-extending property. The mining of Spetrox is controlled by Trau Morgus (John Normington), but his power is threatened by Sharaz Jek (Christopher Gable), a mysterious masked figure who lives in the caves and controls an army of androids who disrupt the mining. In public, Morgus supports General Chellak (Martin Cochrane), who battles Jek, but he secretly funds gunrunners Stotz (Maurice Roeves) and Krelper (Roy Holder) who provide weapons to the rebels. The war increases the price of Spectrox.
The TARDIS lands on Androzani Minor and the Doctor and Peri (Nicola Bryant) explore the caves. They contact a sticky substance. They are captured by Chellak, who thinks they are gunrunners. Morgus does not recognize them and orders their execution. The Doctor and Peri are coming down with a sickness caused by the substance they contacted—raw Spectrox. The only anti-toxin is the milk of the Queen Bat, but the war has driven the bats deep into the mines where the oxygen is thin.
They are put before a firing squad and shot dead. But it seems Jek has replaced them with androids, much to the dismay of General Chellak, who covers up the failure. Jek explains that he is at war with Morgus over his disfiguration, which he hides under a mask. He leaves the time-travellers guarded by his androids while he goes to meet Stotz and Krelper. The Doctor re-programs the androids and they escape. They are caught in a battle and Peri is captured by Chellak, while the Doctor is taken away by Stotz and Krelper.
Stotz displays the Doctor to Morgus, which allows him to see that the Doctor, whom he has been assured is dead, still lives, so the paranoid Morgus believes the military is deceiving him. He throws the Androzani President out the window and calls it an accident, then travels to Androzani Minor. The Doctor commandeers Stotz’s ship and flies it back to Androzani Minor as well to rescue Peri.
Chellak attacks Jek’s androids, at the loss of many of his soldiers, his own androids, and eventually his own life, but in the process rescues Peri before she dies of Spetrox poisoning. The Doctor, also suffering the effects, is told by Jek where he can find the Queen Bat. Morgus lands by Stotz’s crashed ship and finds that he has been deposed back home by his own assistant (Barbara Kinghorn). He makes a deal with Stotz to get Jek’s supply of Spectrox, and Stotz kills Knelper, then Morgus, Stotz, and Jek end up killing each other.
The Doctor finds the Queen Bat and collects two vials of the anti-toxin. Exhausted himself, he carries the unconscious Peri across the desert, and in the process drops one of the vials. He sets the TARDIS in motion and gives Peri the antidote, going without it himself. Peri awakes to find him dying and regenerating. He hallucinates his past companions and the Master laughing, calling out for Adric before he rises as the Sixth Doctor (Colin Baker). Production of this broadcast was interrupted by a strike, and two sequences were cut. Morgus, the mad tycoon, frequently broke the fourth wall and spoke to the audience because the actor, John Normington, misunderstood a stage direction. But he was such a good actor that these scenes sounded like Shakespearean soliloquies and director Graeme Harper decided to keep them. They are arresting and powerful and elevate the entire production. Christopher Gable, who plays Sharaz Jek, was a well-known actor and a leading ballet dancer. In his black and white mask, he creates a Phantom of the Opera vibe and seems totally insane. In fact, most of the characters in the entire serial are cruel and callous and self-absorbed and pretty much mad as a hatter. The story is fast-paced and loud and full of struggle and betrayal and murder, and it all seems like an Elizabethan tragedy. Tim Curry, Mick Jagger, and David Bowie had been offered the role of Jek, and the director was glad they turned it down.
Caves of Androzani was Peter Davison’s favorite story of his three years as the Doctor, and in the 40th Anniversary Poll, in 2009, it was voted the best Doctor Who story of all time by fans. The directing was spectacular. Even the best Doctor Who serials are at times too slow. This one never slows down. It is filled with fighting and shooting and histrionics, and there are three groups of bad guys who end up killing each other. It’s kind of exhausting, actually, but unforgettable. It is the climax of the decades-long Spectrox Wars, with the cold, ruthless Morgus, his former partner Sharaz Jek—brilliant but disfigured and insane—and a brutal crew of gunrunners led by the psychotic Stotz, all casually condemning the Doctor and Peri to death, while the hapless time-travellers are already dying from Spectrox poisoning.
Peter Davison still jokes that his final scene, his death and transfiguration, was upstaged by Nicola Bryant because she leaned over him as he died in her arms and prominently displayed her cleavage to the viewers. The Sixth Doctor (Colin Baker), was also prominent in that scene, as he appeared in full view and spoke lines instead of being relegated to a special effect as in most regeneration scenes. In the future, this would happen a lot as regeneration became more and more spectacular. Incidentally, as promised, the Doctor reveals why he wears a stalk of celery in his lapel: it will change colour in the presence of Praxis-range gas, to which he is allergic.