"I'M TELLING you, there's no anti-matter on this ship," somebody snaps irritably. "And I'm telling you that there is," replies Tom Baker patiently, with one of those smiles that stretches slowly from ear to ear and makes his eyes bulge like golf-balls.

The Doctor and Sarah-Jane (Elisabeth Sladen) have answered a distress call from Zeta Minor, where something unpleasant is picking off the members of a geological team.

This four-parter benefits from a taut storyline and a nicely sustained atmosphere of claustrophobia and lurking menace. Most of the action is studio-based but a couple of filmed sequences give an idea of how things might have looked with a more generous budget.