Shoreditch, London, 1963. Two teachers follow an unnervingly knowledgeable schoolgirl to her home - a blue police telephone box in the middle of a scrapyard. The old man whom the girl calls "grandfather" is annoyed at the intrusion: there is something he has to do, and he has a premonition that he will be delayed for some time...

Six regenerations later the Doctor returns; and Ace, his travelling companion, sees London as it was before the Sixties started swinging — and long before she was born.

But a Grey Dalek is lurking in Foreman's Yard; Imperial Daleks are appearing in the basement of Coal Hill School; and both factions want the Hand of Omega, the remote stellar manipulator that the Doctor has left behind. Has the Doctor arrived in time to deprive the Daleks of the secret of time travel?