The ageless leader of a dying race believes that salvation lies within The Chaos Pool, a place that even the Guardians of Time have been unable to locate. Meanwhile Commander Hectocot and his Teuthoidian followers move in for the kill - again and again and again...

Two different races from opposite ends of Time - so how can they co-exist?

In their search for the final segment of the Key to Time, the Doctor and Amy become caught in the crossfire. As the end of everything approaches, old friends and enemies reveal themselves and the final battle between the forces of Chaos and Order ignites…