The Peter Davison Years 1982-1984
This is the farewell story of Peter Davison, the Fifth Doctor. The Doctor and Peri find themselves embroiled in an underground war soon after arriving on the barren world of Androzani Minor.
As they follow a mysterious trail into some nearby caves, they unwittingly violate General Chellak's military blockade and are summarily sentenced to death as gunrunners. An unexpected rescue by the actual gunrunners throws them into the clutches of the sinister Sharaz Jek, a masked renegade scientist who has gone underground, both figuratively and literally. Jek has amassed a f-rce of lethal androids to guard his subterranean domain. For in the heart of the caves is a rich source of Spectrox - the most valuable commodity in the universe... and in its raw form, the deadliest!
Once the Doctor learns that the mysterious substance he and Peri handled in the caves was raw Spectrox, he realizes time is running out - for Peri as well as himself.