The Third Doctor's Earth-bound exile has been lifted. But before he can set out on new adventures, an alien invasion appears to threaten Earth! It's the devious work of an old enemy, Salamander, a former dictator with a startling resemblance to the Second Doctor! Now, forming an uneasy alliance with the Master, the Doctor and UNIT set out to stop him – but are they too late to stop his plans as he takes them all back into the past.