Doctor Who: Once and Future - Two's Company

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.

Back on Earth, the Doctor finds a clue in the search for the origins of the degeneration weapon. In his Sixth body, he meets Jackie Tyler and Lady Christina de Souza – thrown together by fate, or something more? – in pursuit of a powerful item of jewelry. Meanwhile, a Time Lord renegade has duped Harry Sullivan into helping him stop the Doctor’s travels before they begin – and all are set on a collision course.