Full Circle is the third serial of the 18th season of the British science fiction television series Doctor Who, which was first broadcast in four weekly parts on BBC1 from 25 October to 15 November 1980. The serial involves the alien time traveller the Fourth Doctor (Tom Baker) discovering the life cycle of three closely related species on the planet Alzarius—the humanoid Alzarians, the Marshmen, and the Marshspiders—coming "full circle". Full Circle is the first of three loosely connected serials set in another universe to the Doctor's own known as E-Space and introduces Matthew Waterhouse as the companion Adric. Plot En route to Gallifrey, the TARDIS passes through a strange phenomenon and ends up in an alternative universe called E-Space, where a small but sustainable civilisation of humanoids called Alzarians live between a river and a grounded spaceship, Starliner. It is an oligarchy ruled by three senior colonists known as Deciders. A sudden series of irregular events are interpreted by Decider Draith as a bad omen and the colonists move into the Starliner to protect themselves. One of the younger colonists, Adric, watches Draith drown in the river. His last words are "Tell Dexeter we've come full circle!" Adric heads into the forest in panic, finding the TARDIS, where the Doctor and Romana take him in. The other Deciders order the Starliner sealed and select a new Decider. Humanoid Marshmen and scuttling Marshspiders begin to appear. The Doctor gains entry to the Starliner, followed by a Marshchild. Both are found and taken to the Three Deciders. The Doctor is appalled when chief scientist Dexeter starts to perform vivisection experiments on the Marshchild. Romana is bitten by a Marshspider and starts to change, seemingly possessed. The Doctor uses a protein serum to cure her and they determine the ship has been maintained for 40,000 generations by a species that has three aspects: spiders, Marshmen, and Alzarians. They are all the same species and thus have come "full circle." It is accidentally deduced that oxygen in its pure form is toxic to the Marshmen and this non-lethal defence is used to force the Marshmen out of the Starliner. During their retreat, Adric stows away in the TARDIS as his fellow colonists pilot the craft away from Alzarius. Production The story was repeated on BBC1 (except BBC1 Wales) across four consecutive evenings from Monday to Thursday, 3–6 August 1981, achieving viewing figures of