The Boneheads have gathered at the haunted Bone Manor to go trick or treating. But first they have to stop JP Rothbone & his Sniveling Cronies in their latest diabolical scheme: they want to exterminate the bats! Deep below the mansion, in the hidden bat cave, JP and his cronies have created a machine that will disrupt the bats’ echolocation, trapping them inside the cave forever! With no bats, there will be a plague of mosquitoes, and Rothbone can expect an increase in sales of his faulty bug zappers. Can the dynamic duo, Bonehead and T-Bone, stop JP, rescue the bats, and still have time to go trick or treating?