The Impossible Planet

The TARDIS arrives inside a "Sanctuary Base" used for deep-space expeditions; as Doctor and Rose explore it, they discover strange alien writing that 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 archaeologist Toby Zed, are on an expedition on an anomalous planet, named "Krop Tor", in orbit around a black hole. Zack explains that a gravity well exists around the planet, allowing them to safely enter or leave the event horizon of the black hole, and that it is generated by an immense energy force ten miles within it, 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 planet-quake, causing the section of the base containing the TARDIS to fall into the planet, and the two become resigned to help 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 awaking, while Toby is unknowingly possessed by the Beast and kills a crew member. When drilling is complete, the Doctor offers to go with Ida into the bowels of the planet. After travelling down the shaft, the Doctor and Ida find a large circular disk, inscribed with more undecipherable markings, which the Doctor believes is a door. As they watch, the door begins to open; simultaneously, the Beast repossesses Toby and the Ood. The possessed Toby warns Rose and the remaining crew that the planet is now falling towards the black hole, and that the Beast is free, while the Ood, now claiming to be the Legion of the Beast, begin to close in on them.