A UNIT nuclear convoy, stranded on the shores of Lake Vortigern, becomes the focus of an incursion by knights from a parallel reality. In this other world, technology and magic exist side by side, and the legends of King Arthur are fact. Close to the lake, the sinister Mordred battles against his enemy Ancelyn and summons his mother, the powerful witch Morgaine.
This novel is based on a Doctor Who story which was originally broadcast from 6-27 September 1989.