The story revolves around the lost planet Shada, on which the Time Lords built a prison for defeated would-be conquerors of the universe. Skagra, an up-and-coming would-be conqueror of the universe, needs the assistance of one of the prison's inmates, but finds that nobody knows where Shada is anymore except one aged Time Lord who has retired to Earth, where he is masquerading as a professor at the University of Cambridge. (The story features some lovely on-location filming in Cambridge, all of which was fortunately completed before the strike.) Luckily for the fate of the universe, Skagra's attempt to force the information out of Professor Chronotis coincides with a visit by the professor's old friend the Doctor (and this is where the story really begins...)
Shada is available on video, with the missing sections filled in by commentary delivered by Tom Baker.
Elements of the story were rehashed by Adams for his novel Dirk Gently's Holistic Detective Agency.
In 1983, clips from Shada were used in The Five Doctors, the 20 year anniversary special. Tom Baker, the fourth actor to play the Doctor, had declined to appear in the special, and the plot was reworked to explain the events in the clips.
In 2003, the BBC released a series of Doctor Who animated audio-drama webcasts that are a remake of Shada, starring Paul McGann as the Doctor, James Fox as Professor Chronotis, and Andrew Sachs as Skagra. As of 2003 it is available at BBCi.