Doctor Who: Companion Piece

Escaping from one battle and straight into another, the Doctor and his companion, Catherine, find themselves on a far-flung world where time travellers are persecuted as witches and warlocks by the Holy Inquisition. The Doctor is arrested, his only hope of escape being Cat. But she has demons of her own to face, and as the Doctor starts to realise exactly what is happening, so time rapidly starts to slip away, both for him and Cat.