Kirk and a large landing party beam down to explore the beautiful garden planet of Gamma Trianguli 6. But the planet turns deadly when the party are killed by dart-shooting flowers, exploding rocks, and precision lightning strikes. The party captures one of the primitive locals who insist that their god Va'al rules over the planet... and it is angry with the newcomers who seek to destroy Paradise.

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.