An alien serial killer is sent to Earth to live among humans as punishment. Although the alien's body has been genetically transformed to look human, the procedure is incomplete, and after a while he begins to revert to his original form. After his head explodes, he must "borrow" another from anyone who happens to be nearby. He does so by squeezing the person's head off with a crablike claw and skewering it onto his own neck. The fact that all of the victims' heads have been removed is the only clue police officer Pierce (Rae Dawn Chong) and her partner have in their efforts to stop the killing spree.
