Doctor: David Tennant (Tenth Doctor)
Companion: Michelle Ryan (Lady Christina de Souza)
Lee Evans – Malcolm Taylor
Noma Dumezweni – Capt. Erisa Magambo
Adam James – D.I. McMillan
Glenn Doherty – Sgt. Dennison
Victoria Alcock – Angela Whittaker
David Ames – Nathan
Ellen Thomas – Carmen
Reginald Tsiboe – Lou
Daniel Kaluuya – Barclay
Keith Parry – Bus driver
James Layton – Sgt. Ian Jenner
Paul Kasey – Sorvin
Ruari Mears – Praygat
Directed by James Strong
Written by Russell T Davies and Gareth Roberts
Script editor Lindsey Alford
Produced by Tracie Simpson
Executive producer(s) Russell T Davies
Incidental music composer Murray Gold
Production code 4.15
Series 2008–2010 specials
Length 60 minutes
Originally broadcast 11 April 2009
The burglar Lady Christina de Souza steals a gold chalice once belonging to King Æthelstan from a London museum, and hops on a 200 bus. The Doctor later joins her and the other passengers, just before the bus passes through a wormhole and ends up on the sands of the planet San Helios. The Doctor studies the wormhole and determines that the bus protected them from its effects like a Faraday cage, and is too late from stopping the driver from stepping back through. When the driver's skeleton appears on Earth, UNIT forces are alerted, led by Captain Erisa Magambo and aided by scientific adviser Malcolm Taylor.
The Doctor manages to contact UNIT to coordinate efforts of how to return the other passengers safely to Earth. The Doctor and Christina scout ahead, while the others attempt to repair the bus. The Doctor and Christina spot a sandstorm on the horizon when they are met by two Tritovores, a species resembling anthropomorphic flies, who take them to their wrecked spaceship. They explain they were delivering a shipment to San Helios, which had housed over hundred billion just recently but now is desert wherever they scan. The Doctor has them scan the approaching sandstorm and finds it really is a swarm of stingray-like aliens that are destroying the ecosystem. He suspects they are generating the wormhole to travel to their next planet to feed upon, and they must hurry and close the wormhole before they can reach Earth. Christina uses her burglary skills to obtain a power crystal and its mounting from the Tritovore ship, but accidentally wakes an alien stingray, which consumes the Tritovores.
With the swarm nearly on them, the Doctor uses the crystal's mounting, an anti-gravity device, to enable the bus to fly, but to control it, he forces Christina to give him the gold chalice, which he hammers down to interface the bus's controls with the mountings. They fly back through the wormhole just as Malcolm and Magambo shut it down, but not before three stingrays sneak through, which UNIT quickly dispatch. The passengers are debriefed, while Christina is arrested. She asks the Doctor to take her with him, but he refuses; however, he conveniently allows her to escape back onto the bus and fly off before authorities can stop her. As the Doctor departs, Carmen, a passenger that has low-level psychic abilities, has a premonition that visibly unnerves him:
You be careful, because your song is ending, sir. It is returning, it is returning through the dark. And then Doctor... oh, but then...he will knock four times.
— Carmen, "Planet of the Dead"