"What right do you have to wipe out a whole reality?"

The history of the planet Earth has become splintered, each splinter vying to become the prime reality. But there can only be one true history.

The Doctor has a plan to ensure that the correct version of history prevails — a plan that involves breaking every law of Time. But with the vortex itself on the brink of total collapse, what do mere laws matter?

From the Bristol riots of 1831, to the ruins of the city in 2003, from a chance encounter between a frustrated poet and Isambard Kingdom Brunel, to a plan to save the human race, the stakes are raised ever higher — until reality itself is threatened.