Terra is dying, when a strange man in a blue box comes to comfort her. One moment she has no idea who he is, and the next she remembers - she's known the Doctor her whole life. And he's going to make sure she's never alone.

The cracks in the universe have been dealt with, but the Doctor faces an even bigger mystery - and to solve it, he'll need to make the ultimate sacrifice. The third and final story in a planned "mini-arc" trilogy set within Season 5 of Doctor Who.