Rose and the Doctor land on a base on a planet that is impossible to circle a black hole. The base’s personnel is there as part of an expedition to drill to the planet’s center. They are served by a race of aliens called the Ood. Several parts of the base, including the one where the TARDIS was, sink into the planet after an earthquake hits it. The Ood predict the emergence of a “Beast” that will take control of archeologist Toby Zed and then the Ood as the drill gets closer to the center of the planet. After the drilling is complete, the Doctor volunteers to accompany Ida Scott to the planet’s depths, where they find a disc on the base and the face of the possessed Toby that has illegible markings on it. The Doctor thinks the disc is a door, and as it opens, the Beast’s voice declares his freedom, and the possessed Toby informs Rose that the planet has started to plunge into the black hole.