In the prequel, the Doctor is seen on a spaceship holding a red button to stop the ship from blowing up. He phones the TARDIS to ask Amy to rescue him, and then realizes she’s not there and thinks he’s dead. He lets go of the button and the ship explodes.
Landing on Earth in his spacesuit, he is helped by Madge Arwell (Claire Skinner) and promises to help her someday. On Christmas Eve, 1941, he becomes the magical caretaker to her and her children, Lily (Holly Earl) and Cyril (Maurice Cole). Madge has received a telegram that her husband Reg (Alexander Armstrong) has disappeared over the English Channel, but she will not tell the children until after Christmas.
Cyril opens a large glowing present left by the Doctor under the Christmas tree—a time-portal to a snow-covered forest. He enters. The Doctor follows with Lily and they track Cyril to a structure like a lighthouse. Madge follows the trail of her children but finds three miners in spacesuits. They tell her the forest will soon be melted by acid rain, killing any living thing in it. At the lighthouse, Cyril finds a humanoid creature made of wood. It places a kind of crown on his head. Lily and the Doctor arrive with another wooden creature, but the Doctor and Cyril are rejected as weak (male). The Doctor understands that the crown allows the life forces of the trees to escape the destruction.
Mage reunites with her children as the acid rain starts. She is recognized as strong by the wood creatures, because, as the Mother Ship, she can carry the Life Force. She puts on the crown, absorbing the Life Force of the Forest, and uses the top of the lighthouse as an escape pod into the Time Vortex. Reg’s plane follows the light through the Vortex and lands outside the Arwell House at Christmas. The Life Force of the Forest are now eternal beings in the Vortex. The Doctor joins Amy and Rory for Christmas dinner. They already knew he wasn’t dead because River Song told them.
Scenes were filmed in a real Lancaster Bomber named Just Jane and in the Forest of Dean. The episode was, of course, inspired by The Lion, the Witch, and the Wardrobe by C.S. Lewis, and the wardrobe was the TARDIS. The story took place on Androzani Major, as opposed to the Caves of Androzani with Peter Davison, which took place on Androzani Minor. This was Caroline Skinner’s first gig as Executive Producer. Arabella Weir, who played the miner Billis, was David Tennant’s landlady and an old friend.