"Oh, the Doctor. He's got a brilliant mind. I might let him have it back when I've finished with it."
Having consistantly failed to reach Metebelis 3, the Doctor takes Jo to see the famous Falls of Osmyr. But when they land they quickly find themselves separated — and unwilling participants in a plan for universal dominance.
Whilst Jo tries to escape from a rebel army on Osmyr, the Doctor meets the reptilian Hirathain and their feathered enemies the Ornthax. Why are
both sides so eager to possess the son of the Osmyrian President? And just who really is the Hirathain Head Scientist?