It is the coldest part of winter, the exact midpoint, Christmas Eve – halfway out of the darkness. Amy and Rory find themselves trapped on a stricken spaceliner that is descending through banks of thick icy fog towards the surface of the planet below. The only person who has the power to save them is Kazran Sardick, a wealthy but lonely old miser who rules Sardicktown with an iron fist. He is the only one in possession of a machine that can clear the fog and allow them to land safely.The Doctor realizes that his only chance of rescuing the ship's 4,000 passengers is to save Kazran's soul and show him that life is worth living. To do this, he needs to go back in time to when Kazran was a young boy, full of potential and dreams. Can the Doctor find a way to put a song in Kazran's heart and bring love into his life in time for Christmas? Can he bring him out of the darkness and into the light?