A space liner with Amy (Karen Gillan) and Rory (Arthur Darvill) aboard loses control when passing through electrified clouds over a human-inhabited planet. The Doctor discovers the clouds are controlled by rich and bitter Kazran Sardick (Michael Gambon), who is so mean he refuses to let the ship land. Kazran feared his father, the inventor of the cloud-controlling machine. The Doctor travels to Kazran’s past to change his life. Meeting Kazran as a young boy (Laurence Belcher), he uses his sonic screwdriver to summon a shark that lives in the clouds. The shark eats the screwdriver and falls ill and cannot swim back to the clouds.

Young Kazran takes it to a cryogenics storeroom where his father keeps debtors in storage as security for their loans, including a woman named Abigail (Katherine Jenkins). She sings to soothe the shark and the Doctor uses Abigail’s cryo-unit to transport the shark home. Kazran promises to see her every Christmas Eve. Kazran and Abigail fall in love, but when it is revealed that she has an incurable illness and one day to live, Kazran asks the Doctor to keep her frozen. He becomes embittered and eventually refuses to help the ship.

Old Kazran is visited by holographic images of the ship’s crew and passengers. The Doctor brings young Kazran to the future to see what he becomes. Realizing that he has become just like his hated father, he decides to save the ship. The Doctor has Abigail sing into one-half of the sonic screwdriver, and the other half, in the shark, responds, dispelling the storm and saving the ship. Kazran releases Abigail, if only for one day.

The story was inspired by A Christmas Carol by Charles Dickens. Welsh singer Katherine Jenkins sings the beautiful songs. Arthur Darvill (Rory) becomes an official companion with this story. The producers did not know that Katherine Jenkins had no acting experience, but she was excellent. Writer Stephen Moffat was afraid of sharks as a child and thought they could come out of the water after him. A town was designed with round doors like the Nautilus to look as if it was used to seeing fish flying through the air. The console that controls the planet’s weather reminds me of the organ on board the Nautilus in 20,000 Leagues Under the Sea. The episode was nominated for a Hugo but lost to The Pandorica Opens.

The production didn’t think they could get Michael Gambon and were thrilled when he accepted. He had just appeared as Dumbledore and getting him was a coup. The bridge of the starship was inspired by that of the Enterprise in 2009’s Star Trek. Abigail sings In the Bleak Midwinter by Christina Rossetti and Abigail’s Song, written for her. Kazran was Scrooge, the Doctor was the Ghost of Christmas Past, Amy the Ghost of Christmas Present, and Kazran himself was the Ghost of Christmas Yet to Come, appearing to his young self. The shark was called Clive, Percy, or Clyde, depending, though it was supposed to be female.