An exciting 'lost' television adventure starring second doctor Patrick Troughton with linking narration by Colin Baker. The Doctor, Polly and Ben visit a human colony that appears to be one big holiday camp. They soon discover, though, that its inhabitants have been brainwashed by the Macra, giant crab-like creatures who have taken over the colony. The humans are being forced to mine a gas that is essential for the Macra to survive - but fatal to them. It's a scary race to rescue them, with Ben getting taken in by the Macra for a time, but eventually the time travellers manage to restore the colony's freedom.