Jim awakens one morning to find that his cranium has more than doubled in proportion. Initially embarrassed, it takes Jim nearly a week to leave his apartment, and his first stop is a head specialist. But good Dr. Axel can offer no solid answers, so an irritated Jim heads out the door for home. On his way, he's cornered by a gang of thugs, who have absolutely no idea what's awaiting them. Jim's head splits in two and out jumps a little purple alien who attacks them. After beating up the aggressors, the alien pops back into Jim's head, which seals up behind him. Dumbfounded, Jim heads home and interrogates the alien. Turns out his name's Roy, and he's on a mission to save the Earth from a parasitic alien named Gork. Dr. Lucas Elliott, a disgruntled FBI agent, catches the thugs telling their story on Eye Witness News, and begins his pursuit of Jim.