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.
A sudden series of irregular events culminating in the mysterious "mistfall" are interpreted by Decider Draith as a bad omen, which occurs every fifty years.
After Adric inadvertently leads a small band of outcasts to the TARDIS, they commandeer the ship leaving Romana stranded in a cave filled with Marshspiders.
The two had developed a character document on 30 January, which outlined that Adric was "fifteen, small for his age, wirey [sic] and strong, with short straight black hair."
[2] Bidmead had also previously suggested "a trilogy of stories with a linking theme" to Nathan-Turner, outlining the concept of a parallel universe called E-Space in a document on 12 June.
This was due to the BBC's competitor, the ITV Network, screening Buck Rogers in the 25th Century in the same timeslot, which had severely impacted on the ratings for this season of Doctor Who.
Paddy Kingsland's incidental music for the serial was released as part of the compilation album Doctor Who at the BBC Radiophonic Workshop Volume 4: Meglos & Full Circle in 2002.