The universe stands on the brink of a dimensional crisis - and The Seventh Doctor and Raine are pulled into the epicentre of it. Meanwhile, on Earth, Unit Scientistic Advisor Dr Elizabeth Klein meets another Doctor she's never met before, until they are tested to the limit by a series of bizarre, alien invasions. At the heart of it is a terrible secret, almost as old as the Time Lords themselves, reality is beginning to unravel and two Doctors, Raine, Klein and all of Unit must use all of their strength and guile to prevent the whole of creation being torn apart.