Returning to television after an overlong hiatus (save for a brief "revival" in the BBC radio serial "Slipback"), Doctor Who launched its 23rd season on September 6, 1986. In an unusual move, the producers decided to devote the entire season to a single continuity, with the overall title "The Trial of a Time Lord." The story was subdivided into four chapters, each given its own subtitle (those these subtitles did not appear onscreen), each running between two to four episodes. In "The Mysterious Planet, Episode 1," the Doctor (Colin Baker) is put on trial for his life for breaking the Laws of Time. The Valeyard (Michael Jayston), or chief prosecutor, endeavors to seal the Doctor's doom with selected videotaped examples of the Doctor's "treachery." Doctor Who: The Mysterious Planet, Episode 1 was written by Robert Holmes.
by Hal Erickson synopsis