When a small spaceship crashes into the Pacific Ocean region on Earth it causes an Earthquake, which is felt in the Tomorrow People�s Lab. The spaceship is piloted by two Thargons, Flyn and Sula, who have escaped from the fleet�s main �Thick Ship� in a short-range �Slim Ship�, which they have deliberately crashed into the Earth in order to bury it, and so escape detection from space. Believing the crash to have been caused by a meteorite, Tim traces the impact point to the island of Tarpin, part of the Melosean chain of islands. Mike and Hsui Tai jaunt to the island, but when Flyn and Sula decide to raise the ship to the surface, Hsui Tai is blinded by the engines. Back at the Lab, John repairs Hsui Tai�s eyes. A military airplane spots the �Slim Ship�, and its pilot reports back to the dictator General Papa Minn, who orders Major Marcos to investigate with troops. John, Mike and Hsui Tai return to the island and meet Flyn, Sula and Thing, the ship�s computer, and are told by the aliens that they are on the run from the ruthless Thargon Overlords for opposing the massacre of their slaves. Flyn warns the Tomorrow People that the Thargon Overlords will destroy the Earth when they find Flyn and Sula there.