Doctor Who episode 297: Colony in Space – Episode Five (8/5/1971)
Structurally, Malcolm Hulke is trying to pull off the same trick with Colony in Space that he and Terrance Dicks managed brilliantly in The War Games: materially advance the plot each week, gradually peeling back the layers, and keeping things interesting through a series of reversals. The problem is that The War Games was melodramatic, with vivid characters, locations and fairly momentous revelations. Whereas Colony in Space has characters like David and Robert, a muddy quarry and some caves, and a very serious moral about corporate exploitation.