Max Devlin (Elliott Gould) is the owner and superintendent of a run-down apartment building in Los Angeles. In the opening scene, the tenants in Max's apartment building have long lists of grievances that he ignores, but when a tenant is late paying rent, Max chases him until a blind woman asks Max to help her. He refuses, trips over her cane and falls under a bus. Max's soul descends to hell and is greeted by Barney Satin (Bill Cosby), Souls Manager of the Devil's Council. Barney condemns him to Level 4 of Hell, but offers to restore Max to life for two months, during which time he must sign three innocent souls to take his place, including a young boy named Toby. Max hesitates, but Barney reminds him that level four awaits, and he finally agrees to the pact.Back on Earth, Max's soul returns to his body. He gets a cup of coffee at a diner and believes it was a dream until Barney appears. The other customers cannot see or hear Barney and think Max is talking to himself (a running joke used throughout the movie). As Max pays his bill, he does not see himself in the mirror and Barney reveals that inhabitants of hell do not cast a reflection, and demands signed contracts from the three innocents by midnight on May 15. He explains that Max can transport himself via thought, and will have magic powers with his targets as long as they remain in his direct sight. Max questions what will happen to these people, and Barney promises to collect their souls at the end of their natural lives.At a nightclub, 19-year-old Stella Summers (Julie Budd), awaits her turn onstage, and notices Jerry Nadler, a record company executive, in the audience. Max appears, claims he is good luck and guarantees Stella's success. Onstage, her voice falters until Max focuses his thoughts on her and she becomes an amazing singer. Jerry wants to record a demo song and Stella asks to bring Max for luck.Next, Max transports himself to 16-year-old Nelson Nordlinger's (David Knell) room and discovers the teen's interest in motocross racing. The next morning at school, Nelson asks classmates if he can join them at motocross, but they refuse. Max, driving a car advertising "Max's Mobile Motocross School," offers to train Nelson and they head for the desert. Although Nelson is nervous, Max encourages him and Nelson speeds off on his motorcycle. As Nelson rides up a hill, Barney appears (on a motorcycle) to remind Max that the magic only works if the subject is within his sight, and Max runs after Nelson. Another biker, Big Billy Hunniker, sees Nelson ride and, although the teen falls on the other side of the hill, Billy offers to race him someday. Max catches up with Nelson and orders him to stay within his sight at all times.Another day or two later at a carnival, 11-year-old Toby Hart (Adam Rich) is denied entrance because children under twelve are not permitted without an adult. Max appears, pretends to be Toby's uncle, and purchases tickets. As they try every ride, Max asks what Toby desires most, and learns that the boy's father is dead and he wants Max to take his place. Toby brings Max to meet his widowed mother, Penny (Susan Anspach), who runs a daycare center. Leaving Max outside with the children, Penny admonishes Toby to stop bringing potential suitors home. Outside, the children love "Uncle Max"; however, realizing he is late for Stella's recording session, Max disappears before Penny and Toby return to the yard.Meanwhile, in the recording studio, Jerry wants to quit after 42 disastrous attempts, but Max appears, convinces them to try again and, suddenly, Stella's voice is perfect. Her album is released and she becomes a star, with her manager, Max, receiving 20 percent of her earnings. At a party, with Barney observing, Max asks about her parents and Stella claims to be from Topanga, California, with free-thinking parents, unlike her friends' strict parents. Max asks Stella to sign the contract to sell her soul, but she thinks he is kidding.At a motocross meet, Nelson's classmates are surprised that Max enters the teen in the "expert" category. Max stands atop a trailer to keep Nelson in his line of sight and, when the teen wins over the favorite, Big Billy Hunniker, classmates change his nickname from "Nerd" to "Nerve."Max appears at a tennis court as Penny takes a lesson and Toby worries that his mother will marry the boring tennis instructor. While Toby keeps Penny away from home, Max supervises installation of new playground equipment in their yard. Penny is surprised and agrees to a dinner date. The next day, they take Toby and the daycare children to the beach, and that evening, as Toby pretends to sleep, Max and Penny kiss.During the next month, Barney materializes before Max and begins to pressure him about getting the contracts signed as Max magically transports between Stella's concert tour, Nelson's motocross races, and dates with Penny and Toby. Stella refuses to sign her contact, instating that they do not need a written agreement. Nelson agrees to sign, but notices what he assumes is an error, pointing out that "sole" is misspelled as "soul" and wants it corrected. As Max works to fulfill Toby's desire, he asks what the child will give him in return for being his father. Max writes a contract with "soul" hidden in the list of Toby's promises, but the boy refuses to sign until Max marries his mother.Meanwhile, despite her success, Stella is lonely. In private with Max, she admits that her real name is Stephanie Pepper and she is from Brooklyn, New York. Her parents did not support her dreams and, although she realizes they were trying to spare her feelings, she always felt she could make it. Max insists he is responsible for her success, and she agrees. Barney then appears and thinks it is the perfect time to get her signature, but Max holds back.Later, Toby is dismayed that Max is always gone, and wants to cancel their deal, but Penny accepts Max's proposal. To fulfill his agreement with Barney, Max plans to marry Penny between Nelson's motocross race and Stella's concert on the 15th of May, but is unhappy about the situation. Despite his qualms, Max disguises himself, hides among autograph seekers and holds out Stella's contract for her signature. The moment she signs, Stella feels strange and, upon accepting her Grammy Award, she becomes uncharacteristically rude (with her soul now the property of Barney).At the motocross race, Max pretends Nelson's contract is an insurance document, and promises to change the soul "misspelling." He obtains Nelson's signature and the teen's happy demeanor changes to cold and hostile as his soul now becomes Barney's property. Max weds Penny, then acquires Toby's signature. When his soul leaves his body, Toby becomes sour toward Max, but his mother believes it is due to jealousy. Barney congratulates Max on his freedom, then admits to lying, and reveals he is collecting the three souls at midnight, while Max gets to live out the natural end of his own life before he returns to Hell.When Max revolts and threatens to burn the three contracts, (in the film's most intense and frightening scene) he is transported to Hell where Barney appears before him in full devil regalia and screams at Max of his terrible fate of torment in Hell if he burns the contracts. Max does so anyway, and is immediately transported back to Earth... no longer with any of his "magic property" powers.At first, Max fears that he's just doomed himself to be sent to Hell at the stroke of midnight. Max leaves his own wedding reception and rushes to the motocross race and learns Nelson was injured prior to the race when he tripped over an old lady's cane. Max finds the woman and discovers she is an angel sent to save Nelson.Later, in Stella's dressing room, she thanks Max for inviting her parents to the show. He asks her to cancel the concert, but she refuses to let him take away her confidence.At home, Max informs Toby and Penny that he must leave at midnight, and they will be better off without him. However, when Penny insists she loves him, Max sees his reflection in a mirror and realizes he has won. When he made the right choice concerning the contracts, the devil lost Max's soul. Overjoyed, Max figures out that his one, kind, unselfish act to sacrifice himself for his three victims has deemed him unfit for Hell.The last scene shows Max, Penny, and Toby attending a concert that Stella is giving which she claims is her "farewell concert" to find herself. Nelson is seen sitting in the audience with his new girlfriend. After Stella sings a new song in flawless tone without any magic talent, Max is seen looking upward (as a reference to Heaven) and mouthing "Thank you very much".