A landing party beams down to Pyrus 7 to survey the surface. The Enterprise loses contact with them, then gets a message from one crewman, Jackson, asking to be beamed up. When they do, he's found frozen dead and a voice speaking through him tells them to leave. Refusing to abandon Sulu and Scotty, Kirk, McCoy, and Spock beam down to encounter witches, castles, a black cat, a warlock, and a sorceress, all determined to have them leave.

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.