The Mysterious Planet is the first serial of the larger narrative known as The Trial of a Time Lord which encompasses the whole of the 23rd season of the British science fiction television series Doctor Who. It was first broadcast in four weekly parts on BBC1 from 6 to 27 September 1986. The title The Mysterious Planet is not used on-screen and only appears in the serial's scripts with the four episodes that comprise the story being transmitted as The Trial of a Time Lord Parts One to Four.