The Doctor arrives on Androzani Minor, with his new companion Peri. Investigations begin immediately as they discover tracks leading off to a cavern. As they investigate, the Doctor explains why he's wearing the celery on his jacket. He's allergic to certain gasses and in their presence, the celery will turn purple. As they continue to explore, Peri falls into a web-like substance. The Doctor brushes it off and tells her not to worry, as it's likely to be harmless. They continue to explore until they suddenly find a cache of weapons. It's then they run into General Chellak who accuses them of gun running. The Doctor tries to explain their innocence but Chellak has a duty to do and though not liking to do so, he orders their execution.
Though it seems they are executed, the Doctor and Peri are saved. While waiting for execution, they were rescued by Sharaz Jek, who replaced them with realistic androids. Sharaz Jek is who General Chellak is fighting against because Jek is hording a supply of Spectrox, a substance which, when refined, can prolong life. Infatuated with Peri, Jek's aim was to supply the Spectrox to her and prolong her life, and beauty. It was Jek's guns General Chellak earlier found Peri and the Doctor with.
The Doctor and Peri aren't the only humans keeping Sharaz Jek compnay. Also prisoner is Major Salateen, who currently has an android double working for General Chellak. All three are held prisoner by Jek's security androids, programmed to shoot anyone trying to escape. Feeling his days may be numbered now that Jek has two new humans to keep him company, he breaks out into laughter when he realizes the Doctor and Peri are suffering from Spectrox Toxaemia and are dying. Though they refuse to believe so, Salateen says there is no cure. He can't wait to see the look on Jek's face when he realizes Peri is dying.
Not being human, the Doctor decides to risk escaping and is delighted to find out the android is not programmed to shoot non-humans. His escape is short lived however when he's captured by Stotz, the gun runner for Sharaz Jek. But Stotz is also working for Morgus, the head of the Sirius Conglomerate, the distributors of Spectrox. Morgus is also responsible for the disfigurement of Sharaz Jek. Wanting full control of the Spectrox again, he joins Stotz on Androzani Minor, but he is betrayed by his personal assistant who tells the government of all his illegal dealings. Being on equal terms now, Morgus reluctantly agrees to Stotz demands they split the Spectrox equally.
While being held captive, the Doctor crashes Stotz's ship back on the planet and escapes. He manages to make his way back to Jek and learns there is a cure for the Spectrox Toxaemia. All he needs to do is collect milk from the rare Spectrox bat. While he's collecting the antidote, there is a full out battle between Sharaz Jek, Morgus, Stotz
Major Salateen and General Chellak; no one survives. Once back, the Doctor collects Peri and carries her back to the Tardis. In a rush, he accidentally spills a portion of the bat's milk. Not sure if he'll regenerate or not, the Doctor gives whatever is left of the antidote to Peri. She quickly recovers, but Spectrox Toxaemia forces the Doctor into a regeneration.
WHO: The Doctor (5th)
DEPARTURE LOCATION: Androzani Minor, Earth's Future
REASON FOR DEPARTURE: After contracting Spectrox Toxaemia with Peri, the Doctor acquires only enough of the antidote for Peri. The poison forces a regeneration.