The Time War. The Doctor has been injured and brought to a Time Lord field hospital. His body glows with energy, but this is no regeneration into a future form – instead, the Doctor’s past faces begin to appear as he flits haphazardly between incarnations…

Staggering to his TARDIS, the Doctor sets out to solve the mystery of his ‘degeneration’. Who has done this to him? How? And why? From the Earth to the stars, across an array of familiar times and places, he follows clues to retrace his steps, encountering old friends and enemies along the way. Tumbling through his lives, the Doctor must stop his degeneration before he loses himself completely...

The Doctor responds to a distress call from his granddaughter, Susan, taking him to the Diamond Array: a huge multidimensional space station. Once there, his instability increases, as the Fourth and Eighth Doctors discover the Array’s terrible purpose.

Meanwhile, River Song has made a deadly alliance to try to save her husband. And the truth about the Doctor’s degeneration will finally be revealed.