The Enterprise is taken over by a new crewman, Mr. Norman, who redirects it to a distant planet. He booby traps the controls and the crew is forced to wait and see where they end up. They end up at a planet populated by androids... and their old adversary, Harcourt Fenton Mudd, who wishes to use the Enterprise to get away.

The Doctor returns to a Tibetan monastery which he hasn't visited for 300 years, only to be accused of murder. The legendary Yeti, normally timid and elusive creatures, have suddenly become vicious and savage, and many monks and visitors to the monastery have been killed. The Doctor faces suspicion from the monks and from the British explorer Travers, who's determined to prove that the Yeti exist and initially fears that the Doctor is from a rival expedition. Eventually the Doctor discovers that the savage Yeti are robots, built by an alien Intelligence who has possessed one of the monks. The Intelligence claims that it only wants physical being - but in fact, its new physical form will consume the entire Earth unless stopped.