Cory, a poor Chicago kid with a penchant for gambling, gets a job at a posh Wisconsin resort as a busboy. He takes a liking to glamorous socialite Abby Vollard, who is toying with the affections of rich boyfriend Alex Wyncott.
Sabotaging her motorboat as a ploy to get close to her, Cory swims out to help, only to find Abby's kid sister Jen on the boat instead. She volunteers to assist his effort to win Abby's heart.
Abby mistakenly believes him to be a guest at the resort. She invites him on a trip to New York, but when Cory tries to raise money at a poker game, a guest named Caldwell cleans him out. Abby is offended when she discovers that Cory's only a busboy and walks away for good.
A year later, now in Reno trying to change his luck, Cory crosses paths again with Caldwell, only he turns out to actually be a professional gambler known as Biloxi. An ulcer prevents him from playing, so Caldwell partners with Cory, making him his proxy at the table.
Together they return to Chicago when gangster Ruby offers them a chance to run an illegal casino. Cory sends an invitation to the grand opening to Abby, then slips away with her after fixing it so her fiance Alex can gamble and win. They begin a secret affair.
Cory's behavior grows cruel and calculating, more so after he proposes to Abby and is coldly turned down. Biloxi is disgusted with him and breaks their partnership. Alex, who is now losing heavily at the tables, becomes aware that Abby is carrying on with Cory behind his back. He tips off the cops, who raid Ruby's gambling house. Cory tries to flee, but Alex shoots him in the arm.
Ashamed of his behavior, Cory declines to prosecute. He goes to the airport, where an older and more beautiful Jen unexpectedly shows up and offers to come along.
Tony Curtis as Cory
Martha Hyer as Abby Vollard
Charles Bickford as Jeremiah Des Plains 'Biloxi Caldwell