Patrick Troughton stars as the Doctor in this serial from the fifth series of the popular sci-fi show. When the TARDIS escapes from peril in space into the London Underground network, the Doctor and his companions, Jamie McCrimmon (Frazer Hines) and Victoria Waterfield (Deborah Watling), discover that danger lurks in the British capital, too. A robot yeti, unleashed by the carelessness of Professor Travers (Jack Watling), is wreaking havoc. Can the Doctor find a way to contain the creature and the alien forces lurking in the background?