In league with her boyfriend Los Angeles attorney Vincent Mailer, socialite Brandy Kirby investigates the background of Michael "Lefty" Farrell from his beginnings in an orphanage to a Chicago reformatory to his troublesome stint in the Navy during World War II. Discovering that Mike now lives in Los Angeles, Brandy travels to California to update Mailer on her search. The day after her arrival, Brandy seeks out Mike in the gambling club where he works and, in cahoots with another associate, Todd, has Mike arrested for brawling. Mike is startled to discover Brandy has bailed him out of jail and accepts her ride back to town. Brandy confesses to Mike that she has been looking for him and reveals the possibility of his earning a large sum of money if he agrees to her proposal. Although initially uninterested, Mike agrees to the mysterious proposal due to his strong attraction to Brandy. Mike is taken aback, however, when Brandy discloses that he is to impersonate someone who had the top of his pinky finger severed. When she suggests that he voluntarily smash his finger in the car door to injure his finger, Mike recoils, then when Brandy reiterates how much money is involved, reluctantly goes through with the mutilation. The following evening, Brandy has Mike move from his shabby one room apartment to a beach house, where he can recover and age his wound by soaking it in salt water. Over several weeks, Mike, supervised by Todd, heals and spends time with Brandy. Finally when his hand is healed, Mike meets Mailer, who details his plan with Brandy to have Mike impersonate the long-lost son of wealthy industrialist William McIntyre. Mailer explains that Will and his wife Maida lost their young son twenty-five years earlier in Chicago. Mailer reveals that he is the McIntyres' attorney and has led a fifteen year search for their missing child, who would inherit ten million dollars at Will's death. A few days later, Brandy takes Mike to the McIntyre estate, knowing the elderly couple is out of town. There she relates several personal details learned from Maida about her son's brief life there. Later, Mailer informs Mike that due to Maida's fragile health, they have devised a plan to introduce him to the family through young cousin Kathy McIntyre. Brandy introduces Mike to Kathy, who appears completely indifferent to him. When a second meeting fails to illicit her interest, Mike rashly visits Kathy at home late one evening, only to learn that she harbors a schoolgirl determination to reform him, believing him to be mildly crooked. Mike playfully fosters the relationship with the naïve Kathy, prompting Brandy's jealousy and, in turn, Mailer's. Mike remains deliberately mysterious to Kathy, however, only responding to her personal questions slowly and with great reluctance. When Kathy eventually learns of his past and links that to his severed pinky, she determines to introduce Mike to her uncle Will. When Mike meets Will, he candidly admits that he cannot be his long-lost son and does not wish to give the McIntyres false hope. After Mike also acknowledges his shady past, however, Will is impressed enough by his frankness to ask Mike to move onto the estate while Will has him investigated. Soon after, Mike spends a day with Maida and manages to utilize the personal details with which Brandy coached him earlier. Maida is convinced that Mike is her missing son, and Will agrees, partly because he wants to placate his wife and partly because he has grown fond of Mike. Brandy and Mailer celebrate Mike's acceptance, but Mailer receives a shock when Will tells him that he does not intend to leave any of his money to Mike as it would be corrupting. Mailer later informs Brandy and Mike about Will's statement, them stuns then by detailing his plan to murder Will as soon as Mike is declared his legal heir to insure the inheritance will go through. Later, Mike asks Brandy to run away with him, but she fears Mailer will pursue them wherever they go. Disappointed, Mike determines to try and save Will, provoking Brandy to wonder whether he is really interested in the inheritance after all. Mike separately arranges to meet Brandy and Mailer at the estate just before the McIntyres return from another trip. When Mike informs them he will continue playing the son and foil Mailer's plans, Mailer responds by threatening to summon the doctor who tended to Mike's injured finger. Mike insists he will not allow Mailer to murder Will, but the attorney scoffs and departs. Brandy pleads with Mike to be careful, then follows Mailer down to the pier in time to overhear him informing Todd he means to murder Mike. Hoping to stall for time and knowing that Todd believes Mike cannot swim, Brandy suggests they make it appear like an accidental drowning and pretends to lure Mike outside, where Todd attacks him. Mike fights him off underwater, just as the McIntyres return and Mailer informs Will of Mike's impersonation. In turn Mike describes Mailer's involvement, then produces a dictaphone recording he made of Mailer's earlier murder plan, which he plays for Will. Afterward, Will reveals he long knew of Mike's phony identity because of a full set of fingerprints he found in Mike's Navy records. Will then declines to prosecute Mailer, content to fire him instead. He asks Mike to continue pretending to be the McIntyre heir for Maida's sake, but when Mike admits his feelings for Brandy, Will is content to have Mike visit occasionally. Mailer flees and Brandy and Mike are happily reunited.