Professor Edward Travers (Jack Watling)—anthropologist and explorer—is awakened by the screams of his companion and sees a lumbering hairy creature standing over his friend’s body. The TARDIS lands in Tibet, and the Doctor goes out exploring the Himalayas, hoping to find a monastery he remembers from an earlier visit. Studying a large footprint, he fails to notice a large hairy creature passing behind him. He finds two empty sleeping bags, a broken rifle, and a dead body. He goes on to the Detson Monastery. A party of men come in and the Doctor, found with the dead man’s pack, is accused of murdering him. (The Doctor seems unable to land anywhere without being accused of a crime.) Travers tells him his mission is to find Yeti.
Jamie and Victoria, tired of waiting, leave the TARDIS and find huge footprints. They find themselves trapped in a cave and discover a chamber containing a pyramid of metal spheres. A Yeti turns up, Jamie attacks it with a scimitar with little success, but he causes an avalanche and the companions escape with one of the spheres and head for the monastery.
The Doctor is put on trial and is tied to the doors of the monastery to see if he will control the Yeti, proving that he is in league with them. Jamie and Victoria arrive and convince Travers that the Doctor is innocent. The Yeti attack the monastery, with little result except that one of the Yeti is overpowered. The Doctor discovers that it is a robot, controlled by a metal sphere in its chest. Awakened, it fights its way out of the monastery, killing several of the monks.
The Doctor and Jamie reach the TARDIS and find it guarded by a Yeti. It is inactive and the Doctor removes its control sphere. There is a conspiracy going on in the monastery and Victoria discovers that the master, Padmasambhava (Wolfe Morris) is commanding the robots. He wipes her mind and summons more Yeti. The Doctor helps Victoria to recover her senses and putting together what she knows and what Travers knows, he figures out that the Great Intelligence, which the conspirators obey, is a technologically powerful mind, bending others to its will. With the help of his companions, he defeats the Great Intelligence and destroys the equipment the conspirators are using, plus all the metallic spheres. The TARDIS departs as Travers runs off in pursuit of a real Yeti.
Jack Watling, who portrays Professor Travers was the father of Deborah Watling, who plays Victoria. The mountains of North Wales passed as the Himalayas for the shoot. One of the actors fell hundreds of feet but was saved from death by his foam rubber Yeti costume. Too bad the costume that saved him was so silly-looking and not the slightest bit frightening. Of the six episodes—there was of course much more in the way of complications and running around than found its way into my synopsis—only one still exists.