After being ordered by his evil boss (Robert Vaughn) to create synthetic Kryptonite in order to defeat Superman (Christopher Reeve), computer genius Gus Gorman (Richard Pryor) is stumped when an analysis of the mineral comes up with an unknown component. Looking at a pack of cigarettes, Gus uses tar to substitute for the component. Instead of killing Superman, the faux Kryptonite makes him evil, moody and destructive. He heads to a bar and drinks and alienates his friends. In a return to his hometown of Smallville, Superman (in his alter ego of Clark Kent) finds his still has a spark with old friend Lana Lang (Annette O'Toole), but even she can't stop his transformation. The change literally breaks Superman into a good and evil personality, who battle it out for control over him. Meanwhile, Ross Webster, Gus' boss, has created a super-computer in his quest to contol the world's economy. It's up to Superman to get control of himself and then stop the evil computer in order to save the day.