"The Impossible Planet" is the eighth episode of the second series of the British science fiction television series Doctor Who, first broadcast on 3 June 2006. It is the first part of a two-part story, followed by "The Satan Pit". The TARDIS lands in a base on a planet orbiting a black hole, an allegedly impossible situation that stumps even the Doctor. The base crew are drilling towards a mysterious subterranean power source, to claim the power that keeps the planet in orbit for the good of the Human Empire. However, an ancient evil is down there too, and it is awakened.

The TARDIS arrives aboard a sanctuary base used for deep-space expeditions. The Doctor and Rose explore the area, discovering strange alien writing that the TARDIS is unable to translate, meaning that it is "impossibly old". They are confronted by the Ood, a docile race of empathic servants who work on the station. After a misunderstanding with the Ood, the Doctor and Rose meet the crew of the base, Zack, Ida, Jefferson, Danny, Scooti and Toby. The crew are on an expedition on the mysterious planet Krop Tor, impossibly in orbit around a black hole. Captain Zack explains that a gravity funnel exists around the planet, allowing them to safely enter or leave the vicinity of the black hole. The source of the funnel is an immense energy force ten miles within the planet, which they are drilling towards to understand its power. As the Doctor and Rose are acquainting themselves with the crew, the base is struck by a quake that causes the section of the base containing the TARDIS to fall into the planet. Rose and The Doctor resign themselves to being trapped and begin helping out the crew.

As the drill nears its target, a malevolent presence begins to make itself known. The Ood's translation spheres reveal messages about the Beast awakening, while Toby is unknowingly possessed by the Beast. The possessed Toby kills Scooti when she discovers him surviving outside the base without any protective gear. When the drilling is complete, the Doctor offers to go with Ida into the bowels of the planet. After traveling down the drill shaft, the Doctor and Ida find a large circular disk inscribed with more undecipherable markings. The Doctor believes it to be a door, and they watch as it opens. Suddenly, the Beast repossesses Toby before transferring into all the Ood as they refer to themselves as the Legion of the Beast. With Rose and the remaining crew alerted that the planet is now falling towards the black hole, the Ood begin to close in on them whilst the voice of the Beast declares that it is free.

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