London, 1963. Returning to the scenes of his first televised adventure, the Doctor and new companion Ace play a tricky game of bluff and deceit involving two rival Dalek factions, local soldiers, and the awesomely powerful Gallifreyan artefact, the Hand of Omega...

The Doctor plans to let one of the Dalek factions have the Hand of Omega (but not too easily, of course) while keeping Gilmore and his military men preoccupied in a safe territory, but that plan could be threatened by a mole in their midst and a miscalculation on the Doctor's part.