Newlyweds Jak Barv and Maida Barv go to Decima, the tenth moon of Jupiter, to run an iron mine. They are alone except for the robot labor force, Jak's assistant, Greg Dant, leaving before they arrived. A robot tries to kidnap Maida, forcing Jak to attempt to fight it off. The robots get belligerent. Jak must fight for them. Jak hears Maida cry for help as she is kidnapped by a robot. He runs to save her. Throwing a large boulder at a robot, Jak finds out that Greg Dant is disguised in the robot skin, controlling the others by short wave. Dant had found gold, and tried to get rid of the Marvs.