A transport ship bearing the sacrifices from Aneth breaks down and becomes stranded in interplanetary space, close to a black hole. Outside the ship, the TARDIS materialises. The Fourth Doctor attempts to save the TARDIS from being drawn into the black hole by attaching it to the Skonnan ship with a force field. He and Romana then board the ship, leaving K9 behind. Once aboard they find a cargo of hymetusite crystals and a hold full of young prisoners from Aneth, led by Seth. The Doctor and Romana are captured at gunpoint by the co-pilot, who forces them to fix the ship using a hymetusite crystal. The Doctor returns to the TARDIS to get supplies, and becomes stranded when the ship's engines start. Steering the TARDIS away from the black hole, he travels to Skonnos.