Tom Baker stars as the enigmatic Time Lord in this classic two-part adventure. Arriving on a seemingly deserted Earth, the Doctor, Sarah (Elisabeth Sladen) and Harry (Ian Marter) soon discover a crew of shipwrecked astronauts from a distant Earth colony. Lured there by a fake distress call, the astronauts are being experimented on by the deadly Sontarans in preparation of a full-scale invasion of the planet. Can the Doctor defeat Sontaran Field-Marshall Styre (Kevin Lindsay) and save the world?