It all begins when Slip and Sach try to gain permission to use a local vacant lot for baseball games. The boys make a trip to the mansion of the lot's owners, the sinister Gravesend family. It soon develops that all the Gravesends are looney, and none loonier than mad scientists Derek and Anton. Derek wants to transfer Sach's brain to the body of a gorilla, while Anton wants to use Sach's graymatter for his robot. Meanwhile, Amelia Gravesend makes plans to feed Slip to her carnivorous plant. Along the way, Sach is periodically transformed into a hideous beast, terrifying one and all, including his would-be rescuers Louie, Butch and Chuck.