In 1931, budding author Christopher Isherwood goes to Berlin at the invitation of his friend W. H. Auden for the gay sex that abounds in the city. He falls for street sweeper Heinz, paying medical bills for the boy's sickly mother, to the disapproval of her other son, Nazi Gerhardt.

It’s the deepest part of winter, the exact midpoint, Christmas Eve – half way out of the dark. Amy and Rory are trapped on a stricken space liner that’s plummeting through banks of thick icy fog to the surface of the planet below. Only one man has the power to save them; only one man is in possession of a machine that can clear the fog and let them land safely. That man is Kazran Sardick, a rich but lonely old miser who rules Sardicktown with a sky-mast of iron. The Doctor’s only chance of rescuing the ship’s 4,000 passengers is to save Kazran’s soul and show him that life is worth living. For this he needs to go back, way back, to when Kazran was a boy with a life full of promise. But can the Doctor put a song in Kazran’s heart and love in his life, in time for Christmas? Can he bring him out of the dark?