'You’re on your own, Ace.' The TARDIS is invaded by an alien presence, and is then destroyed. The Doctor disappears. Ace, lost and alone, finds herself in a bizarre deserted city ruled by the tyrannical, leech-like monster known as the Process. Lost voyagers drawn forward from Ancient Gallifrey perform obsessive rituals in the ruins. The strands of time are tangled in a cat’s cradle of dimensions. Only the Doctor can challenge the rule of the Process and restore the stolen Future. But the Doctor was destroyed long ago, before Time began.

The place is Earth. The time is the near future - all too near. Industrial development has accelerated out of all control, spawning dangerous new technologies and laying the planet to waste. While the inner cities collapse in guerrilla warfare, a dark age of superstition dawns. As destruction of the environment reaches the point of no return, multinational corporations and super-rich individuals unite in a last desperate effort - not to save humankind, but to buy themselves immortality in a poisoned world. If Earth is to survive, somebody has to stop them. From London to New York to Turkey, Ace follows the Doctor as he prepares, finally, to strike back.

'Spare no sympathy for those creatures. They were witches, they deserved to die.' A coach crashes on the M40. All the passengers are killed. The bodies carry no identification; they are wearing similar new clothes. And each has a suitcase full of banknotes. A country vet delivers a foal. The mare has a deep wound in her forehead. In the straw, the vet finds a tapered horn. In the darkening and doomed world known to its inhabitants as Tir na n-Og, the besieged humans defend the walls of their citadel Dinorben against mythical beasts and demons. The TARDIS’s link with the Eye of Harmony is becoming ever more tenuous and is in urgent need of repair. But the time machine takes the Doctor and Ace to a village in rural Wales, and a gateway to another world.