Hieronymus Merkin has recently turned 40, and is in the midst of preparing a film that details his life's history and development. Portraying himself as a marionette being controlled by an unseen puppet master, young Merkin is led away from the innocence of youth and into the waiting arms of one woman after another by Goodtime Eddie Filth. With Filth's guidance, Merkin steadily transforms into a self-centered womanizer, save only for the longing he feels for his one lost love, Mercy Humppe. As the producers of his life story scream for him to come up with an ending, Merkin must look back and decide what, if anything, he's learned from his experiences.

Aware that at the age of 40 his life is more than half over, Heironymus Merkin brings his mother and his two children to a deserted beach to show them a filmed account of his life. As a child, he is persuaded by his dying Uncle Limelight, an old vaudevillian, to embark upon a stage career. Under the supervision of his agent, a leering minion of Satan named Good Time Eddie Filth, Heironymus rapidly achieves success, and, despite the objections of Eddie Filth, he marries Filigree Fondle, a young woman whom he has impregnated. While Heironymus is projecting the film, the production crew that helped shoot it arrives on the beach. He continues to dally with other women, however, right up to the birth of his child. When the baby is stillborn, a white-clad Presence appears before Heironymus, just as it did when Uncle Limelight died. To Heironymus' delight, Filigree eventually runs off with another man, thereby leaving Heironymus free to pursue the beautiful Polyester Poontang. Meanwhile, the film crew, the producers, and the writers are fretting because Heironymus has not yet devised an ending for his picture, and also because a trio of film critics are now present at the beach. After impregnating Polyester, Heironymus marries again. While Polyester is bearing him two children, Heironymus takes up with the seductive Mercy Humppe, but when Polyester loses her third child, and the Presence once again appears, Heironymus finally decides that it is time to settle down. With the coming of dawn, the film ends and Heironymus' producers continue to berate him. Then, a police car arrives, and a furious Polyester threatens to divorce Heironymus for keeping their two children out all night.