The Doctor is trapped, alone, powerless and terrified, on the planet Midnight, as Russell T Davies's Bafta Award-winning time-travelling drama continues. Soon, the knocking on the wall begins. Only a woman called Sky seems to know the truth – but as paranoia turns into a witch-hunt, Sky turns the Doctor's greatest strengths against him, and a sacrifice must be made...

David Tennant plays the Doctor and Catherine Tate plays his companion, Donna Noble. Lesley Sharp guest stars.