The Doctor and Mel take a shuttle from Io to Cressida, a former moon of Uranus that has been turned into a spaceship. It has been programmed to make adjustments to the Hub, the communications array located at Uranus. It is also the prime location to watch the collision of the asteroid Maleficent with the surface of Uranus. The Doctor is here to ensure this collision takes place, because in a few billion years, a new life form will be created, partly caused by the events of this collision.