Eugene's best and only friend is Buster, the living embodiment of his twisted Id. A benign little creature, Buster morphs into a nightmarish beast to mete out vengeance to Eugene's enemies. His victims are the only ones besides Eugene who can see Buster, the creature becoming visible at the time of their deaths. The exception is Aloysius Murphy, whose rare brain disorder allows him to see Buster as well. Eugene learns of this and decides Murphy needs to be wiped off the face of the Earth. He tracks him down but learns too late just how uncontrollable Buster really is.