Full Circle (Doctor Who)

"Full Circle" is the fourth serial of the 18th season of the British science fiction television series Doctor Who. It was written by Andrew Smith and broadcast on BBC1 in four weekly parts from 25 October to 15 November 1980.

The serial features the Fourth Doctor (Tom Baker) and Romana II (Lalla Ward), along with their companion Adric (Matthew Waterhouse), who is making his full debut as a companion in this story.

The plot revolves around the TARDIS being pulled into a charged-vacuum emboitment and crash landing on Alzarius, a planet close to E-Space. The Doctor, Romana, and Adric become embroiled in a conflict between the native Alzarian humans, who are in a juvenile state awaiting "Marshman" adulthood, and the Marshmen themselves, who are revealed to be evolved forms of the Alzarian juveniles transformed by the planet's periodic mists.

Key plot points include Adric's encounter with the Alzarian Marshmen and his gradual acceptance of their lifecycle. The story explores themes of evolution, maturity, and the cycle of life and death. It's also notable as the story where Adric officially joins the Doctor and Romana as a full-time companion, stowing away on the TARDIS at the serial's conclusion. The serial's title, "Full Circle," refers to the cyclical nature of the Alzarian lifecycle and the return to a primitive state. The story uses scientific concepts to explain the science-fiction plot elements, reflecting the style of Doctor Who at the time.