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.
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.
In the serial, the Sixth Doctor (Colin Baker) is put on trial by his own people, the Time Lords, accused of meddling in the affairs of Earth far in the future, when it has been renamed Ravolox and relocated light years from its original location.
Much of the story consists of video testimony presented by the prosecutor the Valeyard (Michael Jayston) of the Doctor attempting to stop the robot Drathro from causing an explosion that would threaten the entire universe.
The Inquisitor informs the Doctor he is on trial for conduct unbecoming a Time Lord; evidence will be presented by the Valeyard.
The Doctor is aware that Ravolox was devastated by a fireball, according to official records, but the presence of flourishing plant life makes him suspicious.
Peri, Glitz, and Dibber eventually meet up with the Doctor back at the ruins of Marble Arch, trapped between the tribe and the service robot.
The Doctor and Peri use the opportunity to escape and re-enter the underground complex, aware that the black light generator is now damaged beyond repair, and if it should self-destruct, it could take the whole universe with it.
John Nathan-Turner had actually wanted to switch to OB shooting as early as Peter Davison's first season in 1982, but met with resistance from the directors working on the show at the time, so was overruled.
Therefore, a special effects assistant, Paul McGuinness, who helped design the costume, was called in to physically play Drathro, while Brierley spoke his lines from off-camera.
His new score for the opening theme was the shortest-lived, lasting for this season alone (not counting the unused 1973 version by Delia Derbyshire and Paddy Kingsland).
Patrick Mulkern of Radio Times was critical of the serial: "a dismal last gasp from ailing writer Robert Holmes.
"[7] AV Club's Christopher Bahn said: "'Mysterious Planet' never really takes off, laden down by the script, a lot of time wasted running around in the forest or down corridors, and some atrocious acting by some of the minor characters, particularly Joan Sims as Katryca, the Boadica-esque warrior queen who sounds like she's escaped from a community-theater Shakespeare in the Park production.