The TARDIS materialises inside a "Sanctuary Base" meant for deep-space expeditions. The Doctor and Rose discover an inscription scribbled on the station wall which the TARDIS is unable to translate.
After a slight misunderstanding when first meeting the Ood, a docile race of empathic servants who work on the station, the travelers meet the crew of the base, led by acting Captain Zachary Cross Flane. The crew, which includes Science Officer Ida Scott, Head of Security Mr Jefferson, and archeologist Toby Zed, are on an expedition on an anomalous planet in orbit around a black hole. The Doctor realises that it is impossible for the planet, which is called Krop Tor, to be in geostationary orbit around the black hole, as it should be pulled in like the star systems around it are. He calculates that it would take a phenomenal amount of power to generate the huge gravity funnel stabilising its orbit. The funnel is not a natural phenomenon, and the crew is drilling ten miles underground to the core of the planet in hopes of finding the power source and using it. The origin of the power source is an ancient civilisation that had been on Krop Tor, and the inscription on the wall is a transcription of a stone tablet found on the planet.
The Doctor soon discovers that storage sections 5 through 8 had collapsed as a result of the earthquake-like tremor they had experienced moments after their arrival, dropping the TARDIS, which had been in Storage 6, into a crevasse. With no resources to divert the drilling, Rose and the Doctor are stranded.
It isn't long before a malevolent presence begins to make itself known. Strange messages about the Beast awaking to make war against God emanate from the Ood's translation spheres and the base computer's speakers. Toby begins to hear voices just before he is possessed by the Beast.
The team finally manage to drill down to the core of the planet. The Doctor and Ida journey down the mine shaft and into a massive cavern with ancient giant sculptures along its walls. They head for the power source, guided by sensor readings, and find a large circular disk set in the floor of the cavern, which the Doctor suspects is a trap door of some sort. The edge of the disk is also covered with inscriptions.
Meanwhile in the base, the Ood's telepathic fields rise dangerously to Basic 100, which is high enough to induce brain death, but they are obviously still alive. Finally the beast makes itself known through Toby before seemingly transferring itself to the Ood. The Ood identify themselves as the Legion of the Beast and begin to advance on the crew members, including Rose. All this coincides with the opening of the trap door as the cavern begins to shake and debris rains down. Zack warns everyone that the planet's gravity field is fading and that the planet is heading straight for the black hole. The voice of the Beast speaks through the Ood, and down below, the trap door fully opens.
Doctor David Tennant (Tenth Doctor)
Companion Billie Piper (Rose Tyler)
Danny Webb – Mr. Jefferson
Shaun Parkes – Zachary Cross Flane
Claire Rushbrook – Ida Scott
Will Thorp – Toby Zed
Ronny Jhutti – Danny Bartock
MyAnna Buring – Scooti Manista
Paul Kasey – The Ood
Gabriel Woolf – Voice of the Beast
Silas Carson – Voice of the Ood
Writer Matt Jones
Director James Strong
Script editor Simon Winstone
Producer Phil Collinson
Executive producer(s) Russell T. Davies
Production code 2.8
Series Series 2
Length 1st of 2-part story, 45 minutes
Originally broadcast 3 June 2006