A reluctant Solomon (Colin Baker), along with his former associates Egan (David Troughton) and Saul (John Wadmore), have (they think!) escaped Earth and returned to their own dimension. But a mysterious force returns them to Earth and drops them right into the middle of a top-secret experiment involving a young girl's mind powers. They soon find that the experiment has gone wrong and unleashed something deadly...and unless they can find a way to stop it, they and the experiment's team members will all soon be dead!

The Stranger (Colin Baker), still stranded on Earth, has escaped his pursuers and found a safe haven under an assumed name. But his former associates want him back and are not giving up the chase so easily, and his lost past is about to catch up with him...