Doctor Who: Mysterious Planet — Terrance Dicks

The TARDIS has been taken out of time and the Doctor has been brought before a court of his fellow Time Lords. There the sinister Valeyard accuses the Doctor of breaking Gallifrey's most important law and interfering in the affairs of other planets.

If the Valeyard can prove him guilty, the Doctor must sacrifice his remaining regenerations. To prove his case the Valeyard focuses on an adventure set in the Doctor's past.

It is an adventure set on the planet Ravolox, a seemingly primitive world but one which the Doctor and Peri find strangely familiar...