Corpse Marker

The Doctor and Leela arrive on the planet Kaldor, where they find a society dependent on benign and obedient robots. But they have faced these robots before, on a huge Sandminer in the Kaldor desert, and know they are not always harmless servants. The only other people who know the truth are the three survivors from that Sandminer - and now they are being picked off one by one. The twisted genius behind that massacre is dead, but someone is developing a new, deadlier breed of robots. This time, unless the Doctor and Leela can stop them, they really will destroy the world.