It's Christmas Eve, 2007. High above the Earth a spaceship is transporting voyagers from the planet Sto to experience the festive period on the planet below. The spaceship is themed in the style of the White Star Liner, RMS Titanic, and much of the ship's decor resembles the original ship that famously sank after being hit by an iceberg. Passengers and crew are dressed in replica costumes from 1912. The Doctor joins the passengers on board and befriends a waitress, Astrid Peth. After a visit to London via the ship's transmit system, the Doctor and Astrid return to the spacecraft just before it is hit by a meteor, causing severe damage and huge fatalities. The Doctor, Astrid and a band of survivors must travel across the ship to the Bridge to prevent the Titanic from crashing into the Earth. Meanwhile, the Heavenly Host (the on-board tourist information robots) are malfunctioning and killing the remaining survivors. Who will survive the voyage?