The Doctor and Romana visit Earth to visit an old Time Lord, Professor Chronotis, who left Gallifrey and became an academic at St. Cedd's College in London. Being an academic means that Professor Chronotis is often visited by students wanting to borrow someof his books, which is he happy for them to do.
A scientist by the name of Skagra is trying to locate on particular book which Professor Chronotis has in his library: The Worshipful and Ancient Law of Gallifrey. With the aid of a device, which resembles a floating grey sphere, Skagra tries to steal the mind of Professor Chronotis and learn the location of the book.
The book, which had been borrowed by Chris Parsons, is the key to the ancient Time Lord prison planet Shada. Skagra's intention is to find one particular inmate, Salyavin, whose mental powers could be exploited to project Skagra's mind into every living creature in the Universe.
Arriving at Shada, Skagra finds Salyavin's cell empty. The Doctor, Romana, K-9, Chris Parsons and Claire Keightley arrive at Shada in Chronotis's TARDIS. After a battle with the Krargs, servants of Skagra, Chronotis reveals that he is Salyavin. He had escaped from Shada and lived on Earth.
After a battle of wills between the Doctor and Skagra, Skagra is defeated. Everyone returns to Earth where Chronotis continues to live.
- Voice of K-9: David Brierley
- Romana: Lalla Ward
- Professor Chronotis (Salyavin): Denis Carey
- Skagra: Christopher Neame
- Chris Parsons: Daniel Hill
- Clare Keightley: Victoria Burgoyne
- Ship: Shirley Dixon
- Wilkin: Gerald Campion (1-3, 6)
- Caldera: Derek Pollitt (1,4)
- Passenger: David Strong (1,4)
- Themselves: St. Johns Choristers (2+reprise 3)
- Voice of the Krargs: James Coombs (4)
- Police Constable: John Hallett (6)
- Krargs: Harry Fielder, Lionel Sansby, James Muir, Derek Suthern, Reg Woods
This programme does not have any original transmissions
Episode 2 : When K-9 checks Chronotis's vital signs and proclaims him to be dead, but you can clearly see Denis Carey's chest rising and falling as he breathes.
Episode 2 : Notice that when Professor Chronotis is being attacked by the sphere, he keeps alternating between wearing and not wearing his eyeglasses - depending on the camera angle.
Episode 2 : Romana calls Chris Parsons by his first name despite not having been told what it is yet.
Episode 3 : Skagra takes Romana into the TARDIS but he forgets the TARDIS key in the door, which remains there as it dematerialises.
This story was scheduled to conclude season seventeen, but a BBC strike meant that it was not completed and never transmitted. The completed footage, which includes all the location work and some studio blocks, was preserved. Because no end titles were produced for the story it is impossible to say which cast members would have been uncredited.
Two scenes from the story were used in The Five Doctors in 1983.
In 1992 a BBC video of the story was released, produced by John Nathan-Turner. This featured added video effects, sound effects (by Dick Mills), incidental music (by Keff McCulloch) and the missing material narrated by Tom Baker. Episode credits as used above are for the story had it been finished and not this video version. The video also includes a copy of the original script.
In 2002 Big Finish re-recorded Shada with Paul McGann as the Doctor, and Lalla Ward and John Leeson reprising the roles of Romana and K-9.