An alien terraforming device lands on Earth and begins to terraform in a graveyard, creating a swamp-like environment. The Doctor and Rose follow it to Earth, where they meet Raj and Jim, who came to the graveyard after seeing the device's flashing lights. Skeletons begin to crawl out of the ground, and the group seek refuge at a nearby house, the home of Ivy Henson, who the two boys believe to be a witch.