Robert is worried. His pet gerbil, Exterminator, is lying on the bottom of his cage, not moving. A trip to the veterinarian's office doesn't help, and soon, Extermie is gone. Robert is so crushed that he can't even talk about it. It doesn't help that his bossy cousin Mabel keeps telling him how he should feel. Or that his older brother, Sam, can't seem to stop telling bad dead gerbil jokes.

Things get even worse when Sam comes up with a plan to cheer Robert up -- a plan that involves a creepy store called Weird Science and its even weirder owner. And one dark stormy night, Sam and Robert find themselves right in the middle of ...the night of the living gerbil!