Frank tends the rubbish heap in the monster realm, just on the other side of the human world. In his spare time, he builds inventions out of scraps of rubbish. One of his inventions is of a human-inspired robot, with a stained t-shirt as the body. But Frank can't seem to get the robot to work. One strange night, a bolt of lightning transforms the invention into a real human child! Frank names him Stain. Curious and energetic, Stain wreaks havoc on the monster realm, angering the monster population. Can Frank save Stain from destruction by convincing the rest of the monsters that Stain is not a threat?