To assure a Kentucky Derby victory for his horse Sarcasm, superstitious New York horse owner and gambler Joe Baldwin, who believes that luck can be bought, agrees to finance an expensive European voyage for Jean Jason, his unfaithful "good luck charm." He also gives Frank Brent, an old friend, $3,000 to save his cab business and visits a Louisville orphanage with his sister, Agnes White. At the orphanage Joe meets pretty Betty McKay, a teacher who scoffs at his "charity-for-luck" philosophy and berates him for wishing for rain on Derby day, which is also the day that the orphans are to have an outdoor party. Although it rains as wished, Sarcasm, the favored "mudder," loses the Kentucky Derby, and a depressed Joe becomes convinced that his horse was jinxed by the orphans. To counter the jinx in time for the Preakness, Joe throws a lavish party for the orphans and hires clowns and other variety acts as entertainment. The party thrills the children, and to Betty's surprise, Joe as well. After Sarcasm wins the Preakness, Joe decides to return to Louisville and pursue a romance with Betty. Jean, who is unaware that Joe has fallen in love with Betty, returns from Europe with her artist lover Paul. When Joe finally returns to New York and tells Jean that he is terminating their arrangement to marry Betty, she demands $50,000 as a final "luck insurance" payment. Before Joe shows up with the check, however, Paul arrives at Jean's apartment and, during a heated fight over the money, kills her. As he is leaving Jean's building, Paul gives an unsuspecting Joe his matchbook, then calls the police and, posing as Joe, "confesses" that he murdered Jean. Joe is tried and convicted of Jean's murder but escapes before his final lockup. With the help of Betty and the grateful cab driver Frank, a fugitive Joe tracks down Paul and convinces the police to question him. By matching partial finger prints from the crime scene to those left by Paul at the police station, Paul is implicated in the murder and finally confesses. Sure now that he cannot buy luck, Joe embraces Betty.