Joe Pendleton, a talented amateur boxer affectionately known as "the Flying Pug," is on his way to a fight in New York City when tragedy strikes. On May 11, 1941, during a routine flight in his small aircraft, a control cable unexpectedly severs, causing him to crash. Sadly, Joe does not survive the accident, but his story is far from over.
His soul is immediately retrieved by an officious angel named Mr. Jordan, who initially believes Joe couldn't have survived the crash. The angel's assistant, a somewhat rigid and bureaucratic figure, informs Joe that due to a mistake, he is supposed to live for another 50 years. However, since Joe's body was destroyed in the crash, Jordan explains that his soul must take over a newly deceased person's body to continue living.
In the afterlife, the records confirm the mistake—Joe was meant to live longer—and Jordan assures him that when he inhabits the body, he will still be himself inside. Joe, however, is determined to continue his boxing career and insists on choosing a physically fit and suitable body. He requests that his new form be someone capable of fighting, which leads to a series of considerations. Initially, Jordan shows him several candidates, but Joe remains unconvinced until they visit the body of Bruce Farnsworth, a corrupt and wealthy banker who has just been drugged and drowned by his wife Julia Farnsworth and his secretary Tony Abbott in a murder plot.
Despite his reservations about inhabiting such a morally compromised life, Joe’s decision is swayed when he witnesses Farnsworth’s cruel treatment towards Bette Logan, a young woman whose father's name Farnsworth misused to sell worthless securities. This act of cruelty finally convinces Joe to take over Farnsworth’s body. As Farnsworth, he begins stripping away the dishonesty of his previous life—returning stolen money, clearing investors’ debts, and ensuring justice for Bette, played by Evelyn Keyes.
Joe, now in Farnsworth’s body, reaches out to his old manager, Max "Pop" Corkle (played by James Gleason), and convinces him that he is still Joe using their shared musical past—playing a saxophone badly, as a familiar sign. With Farnsworth’s resources, Corkle trains Joe for a scheduled fight to determine the next challenger for the heavyweight championship.
However, Mr. Jordan returns unexpectedly to warn Joe that his future as a champion will not occur in the way he hopes. Joe is just about to accept his destiny when he meets Bette Logan again and, in a heartfelt moment, warns her that if a stranger—especially a boxer—approaches her, she should give him a chance. But before he can act on this, he is shot by Tony during a confrontation.
Joe's soul once again returns to a ghostly existence, and Farnsworth’s body is hidden away, with everyone believing he has disappeared. Corkle, believing Farnsworth is missing, hires a private investigator to find him.
With the help of Mr. Jordan, Joe then ventures to retrieve his saxophone from Farnsworth’s mansion—only to discover the police interrogating everyone there about the missing wealthy man. Corkle, lost and confused, inadvertently reveals details about Joe and the angel’s involvement. Using his mental influence, Joe prompts Corkle to turn on the radio just in time to hear the championship fight—where he learns that Joe Murdock has been knocked out from a minor injury but was actually shot by gamblers who tried to force him to throw the fight.
Seizing the opportunity, Joe takes over Murdock’s body, fights valiantly, and wins the boxing title. Back at the mansion, Corkle notices a missing saxophone, piecing together that Joe has switched bodies again—this time with Murdock.
Corkle rushes to the dressing room, where Joe, now in Murdock’s body, reveals to him that Farnsworth’s body is in a refrigerator in the basement of the mansion—an act of misdirection to cover up his murder. The police swoop in, arresting Julia and Tony on the basis of this evidence. Meanwhile, Joe, as Murdock, dismisses his crooked manager and hires Corkle as his new trainer.
Throughout this process, Mr. Jordan explains that this is his ultimate destiny: to be the champion and live life to the fullest, regardless of the body he inhabits. As Joe heals his old injury while simultaneously losing his memory of his previous life, Jordan lingers to see his completion. Eventually, Bette arrives, expecting to meet Corkle but instead encounters Murdock. The two feel an inexplicable familiarity, as if they have met before, hinting at a deeper connection.
In the final moments, Mr. Jordan offers a warm farewell, smiling as he says, "So long, champ," acknowledging that Joe’s journey as a fighter has truly begun. The film closes with the idea that, despite the body he inhabits, Joe's true self remains resilient and ready for the future, blending themes of fate, identity, and the pursuit of one’s dreams.
