It's the 25th Century and the President is being blamed for Earth running out of fish. Meanwhile... Detective Inspector Capstan and Lieutenant Dewbush have somehow managed to prevent the destruction of their home planet by the Mammary Clans. With a much deserved day off, they decide to visit the British Museum where the last ever fish finger is the key exhibit. But it's about to be stolen, and the evidence leads them to Ganymede, a moon orbiting Jupiter,...