Written by Douglas Adams as his final contribution to Doctor Who, Shada was envisaged as a Time Lord story without a Gallifreyan setting. It sees the Doctor bringing Romana to present-day Earth to visit Professor Chronotis, an elderly Time Lord who absconded from Gallifrey and now lives a quiet academic life at St Cedd's College in Cambridge. Also seeking Chronotis is a scientist called Skagra who has a device, in the form of a floating sphere, with which he intends to steal the Professor's mind and thereby learn the location of a book entitled The Worshipful and Ancient Law of Gallifrey. Skagra eventually succeeds in obtaining the book, which has been borrowed from the Professor's study by a student named Chris Parsons. He then kidnaps Romana and hijacks the TARDIS.
Shada was formally dropped from the seventeenth season in December 1979, it having become apparent that due to the backlog of Christmas specials waiting to be recorded there was no prospect of studio time being found for its completion. A number of attempts were subsequently made to remount it but these ultimately came to nothing, and in June 1980 it was officially cancelled. A version of the story was eventually released on video in 1992 with Tom Baker providing a narration to cover the missing scenes.
This "lost episode" is the only Doctor Who television story never to be broadcast.
And we're giving away three copies.