Sylvester McCoy makes his first appearance as the venerable Doctor, coming up against his old enemy, renegade Time Lord Rani (Kate O'Mara). She forces the Tardis to crash land on Lakertya, and then masquerades as his assistant Melanie (Bonnie Langford), tricking the newly regenerated Doctor into constructing a giant time manipulator designed to drain the minds of history's greatest scientists.