When one of the Artefacts of Gallifrey - a dangerous book dating back to the time of the all-powerful Rasillon - goes missing from his study, Cambridge professor and retired Time Lord Dr. Chronotis calls in the aid of the Doctor and Romana. The Doctor is very worried. Who knows what powers could be unleashed if the book falls into the wrong hands?

Then the mysterious Skagra arrives, armed with a thought-draining sphere and a scheme for one universal mind. But first he must get hold of the book...