Doctor: David Tennant (Tenth Doctor)
Companion: Kylie Minogue (Astrid Peth)
Geoffrey Palmer – Captain Hardaker
Russell Tovey – Midshipman Alonso Frame
George Costigan – Max Capricorn
Gray O'Brien – Rickston Slade
Andrew Havill – Chief Steward
Bruce Lawrence – Engineer
Debbie Chazen – Foon Van Hoff
Clive Rowe – Morvin Van Hoff
Clive Swift – Mr Copper
Jimmy Vee – Bannakaffalatta
Bernard Cribbins – Wilfred Mott
Nicholas Witchell – Himself
Paul Kasey – The Host
Stefan Davis – Kitchen Hand
Jason Mohammed – Newsreader
Colin McFarlane – Alien Voices
Ewan Bailey – Alien Voices
Jessica Martin – Voice of The Queen
Directed by James Strong
Written by Russell T Davies
Script editor Brian Minchin
Produced by Phil Collinson
Executive producer(s) Russell T Davies
Incidental music composer Murray Gold
Production code 4.X
Length 72 minutes
Originally broadcast 25 December 2007
The episode opens immediately following the events of "Time Crash", with the bow of the Titanic crashing into the TARDIS. The Doctor repairs the damage before landing the TARDIS on the ship. He discovers it's not the famed RMS Titanic, but instead is a starliner hailing from the planet Sto.
The Titanic is orbiting present day Earth to observe the traditions of primitive cultures, specifically Christmas. The Doctor dons a tuxedo and joins the reception on board, meeting waitress Astrid Peth. The Doctor convinces Astrid to join him on a brief excursion to the surface of Earth. They are accompanied by married couple Morvin and Foon Van Hoff, a Zocci named Bannakaffalatta, and historian and guide Mr. Copper. While on Earth, specifically a commercial district of London, the Doctor notes that London seems abandoned, and questions a man in a newspaper stand about it. The man, Wilfred Mott, tells the Doctor that most people have left London because of the previous two years of alien activity in London on Christmas ("The Christmas Invasion" and "The Runaway Bride").
Back on the Titanic, Captain Hardaker dismisses the ship's officers from the bridge. Citing regulations, that require at least two officers remain on the bridge at all times, Midshipman Alonso Frame stays. After the group returns from their excursion, Hardaker drops the vessel's protective shielding and magnetises the hull. This causes nearby meteors to be pulled toward the ship on a collision course. Midshipman Frame attempts to reactivate the shields but is shot by Hardaker as the meteors collide with the ship. The collision causes hull breaches, most of the 2,000 passengers and staff are killed, and the vessel begins plunging toward the Earth. The Doctor makes contact with the wounded Midshipman Frame, who stabilises and maintains the power from the damaged engines.
The Angel Hosts as shown at the Doctor Who Experience.
The Doctor and the rest of the excursion party attempt to reach the bridge but are repeatedly attacked by the ship's Angel Hosts, androids resembling angels who were programmed to supply information but are now eliminating all passengers and crew. Morvin falls off of a ledge into the ship's engine, and the rest of the group are surrounded by Angel Hosts. Bannakaffalatta reveals that he is a cyborg, and uses his internal EMP device to disable the Hosts. The EMP burst drains the Zocci's power cells and he dies. Mr. Copper takes the EMP device, saying that if they can manage to recharge it, they can use it against the Hosts again. A lone Angel Host attacks them again, and Foon ties herself to it and throws them both into the ship's engine. The Doctor separates from the rest and attempts to reach Deck 31, where he hopes to find the controls for the Heavenly Hosts. He convinces the Hosts that he is a stowaway - neither passenger nor crew and thus not in the Hosts' kill mandate - and the confused androids take him to see their operator, Max Capricorn. Max explains that he planned the Titanic's inevitable collision with Earth to bankrupt the company that voted him out. To save the Doctor, Astrid uses a forklift to ram Max Capricorn and push him into the ship's engine. The forklift falls into the engine on top of him, seemingly killing Astrid as well.
With Max Capricorn dead, the Heavenly Host divert to the next highest authority, the Doctor, and aid him in quickly reaching the bridge. Together with Midshipman Frame, he uses the heat from the entry into the Earth's atmosphere to restart the ship's auxiliary engines. The ship stabilises and narrowly avoids a collision with Buckingham Palace. The Doctor then realizes that Astrid was wearing a teleport bracelet when she fell into the engine. In an emergency, the teleport bracelets were programmed to hold a person's molecular pattern in stasis until it can be recovered. The Doctor frantically attempts to retrieve Astrid's pattern, but the machine is too badly damaged. The Doctor reluctantly allows the ghostly remains of Astrid's atoms to dissipate into space. As the surviving passengers wait for rescue, the Doctor and Mr. Copper, who would otherwise be sent to prison for committing fraud in order to get a job with the company, teleport to Earth and find that the TARDIS has landed unharmed in an snowy field, thrown from the ship after the collision. Mr. Copper is left to live on Earth with a credit card preloaded with a million pounds, thanks to the Doctor.