Major Terry O'Neill, William Powell, returns to Baltimore in 1919, after the end of World War I, hoping to reclaim his old newspaper night editor job. But the paper has recently changed owners, the post has been filled, and his friend and former editor, Allan Smith, Will Wright, has been told to cut costs. Disillusioned, Terry decides to abandon his ideals and make his fortune by whatever means necessary. Leaving the building, he runs into two less-than-savory friends, Fishface, Rags Ragland and Three Finger, Frank McHugh. When the pair are arrested for bookmaking, it takes all his money to pay their fines and that of Snarp, James Gleason.
He crashes a high-society wedding party in the hope of meeting businessman Lewis J. Malbery, Henry O'Neill. When a guard insists on seeing his invitation, Terry grabs guest Kay Lorrison, Esther Williams, and kisses her, much to her surprise. After the guard goes away, she slaps Terry, but after his honest confession, begins to warm to him. She introduces him to her uncle, publisher Joe Lorrison, Charles Trowbridge. Terry impresses him with his ideas on how to fight a bitter foe – none other than Malbery – and lands a job. He and Kay, who works on occasion at the paper, develop a relationship.
After masterminding a skillful newspaper campaign against Malbery, Terry surprises his boss by quitting his relatively low-paying job to go to work for Malbery in New York. Snarp, Fishface, Three Finger and Eel, Slim Summerville, tag along and open a pool room. When after three years, Malbery promotes him to executive vice president of the company, he returns to Baltimore to see Kay. He finds her once again at a wedding. To his dismay, however, she informs him that this time she is the bride. Nightclub singer Dusty Millard, Angela Lansbury, gets him on the rebound.
After a while, Terry crosses paths with Kay once more. She is a widow, and interested in picking up where they left off. Dusty, Angela Lansbury, gives up, realizing she has no chance against her rival. However, Kay learns that Terry has become hard and cynical. When Snarp's bookmaking operation was uncovered, his disreputable pals appealed to Terry; he secretly had Snarp freed, but saw to it that his good fortune was attributed to Saint Dismas.
Terry loses everything in the Wall Street crash of 1929. Nearly all his friends and associates, who invested in the stock market on his advice, make him a scapegoat. The only exceptions are Snarp and Dusty. A reformed Snarp tries to get Terry to put his faith in Saint Dismas, without success. Dusty offers Terry an expensive bracelet he once gave her, but he turns her down. Embittered by the rejection, she takes over a charity Snarp set up dedicated to Saint Dismas, intending to steal the donations and place the blame on Terry.
When Terry leaves town on business, he falls ill and is cared for by Father Nolan, Lewis Stone. Snarp comes to see him to tell him what Dusty and their old associates are doing. Then a concerned Kay shows up. Terry drives into town to plead with Dusty to return the money. Dusty and the others are unmoved at first, but when they see how sincere he is, Dusty gives it all back, and more.
