Arriving on the barren world of Androzani Minor, the Doctor and Peri find themselves embroiled in a long-running underground war. Military troops mount an armed blockade whilst gunrunners bring in weapons for the sinister, masked renegade, Sharaz Jek. Meanwhile, lethal androids guard the caves, and a deadly creature lurks in the shadows, killing all in its path. At the heart of the conflict is a substance called Spectrox - the most valuable item in the universe...and the deadliest! The very presence of the Doctor and Peri on Androzani sets in motion a chain of events that will have dramatic consequences for everyone involved. As the situation gets even more desperate, the Doctor realises time is running out - both for Peri and himself. Will the Doctor make the ultimate sacrifice to save his young friend's life...?