Eager to marry his devoted secretary, Diane Levering, New York shipping magnate Richard Field asks his wife Louise, who has been living overseas for five years, for a divorce. The socially ambitious Louise, however, refuses to give up her position to Diane and denies Richard's request. Although Diane insists that she will continue to love him without the benefit of marriage, Richard asks her to contemplate her choices while cruising to South America on one of his boats. Diane agrees to the cruise, but vows to return to New York unchanged. Soon after sailing from New York, Diane meets Johnny Smith in the ship's bar and firmly rejects his flirtations. Determined, Johnny asks his smooth-talking best friend, Mike Bradley, for help, but is double-crossed when Mike treats him like a masher in front of Diane. Mike's victory is short-lived, however, as Diane later overhears him laughing about his betrayal with the piqued Johnny. In spite of his inauspicious start, Mike soon ingratiates himself with Diane, and a shipboard romance blossoms. Still true to Richard, Diane makes no commitments to Mike and declines his invitation to visit him on his ranch in Buenos Aires. Mike nevertheless shows up at her Buenos Aires' hotel and insists that she join him at his ranch. After a fun-filled day on the ranch, Diane and Mike confess their mutual love, and Diane finally tells Mike about Richard. Realizing that Mike is the man she truly loves, Diane promises him that when she returns to New York, she will end her affair with Richard. However, as soon as she sees Richard, he presents her with a wedding ring and explains to her that his wife finally agreed to divorce him on condition that he not be allowed to see his sons. Overwhelmed by Richard's sacrifice, Diane says nothing about her cruise and, after writing a "Dear John" letter to Mike, marries the millionaire. A year later, Diane runs into Mike in a New York gun shop and suggests that they dine together. In spite of his bitterness, Mike finds that he still loves Diane and senses that she still loves him. Finally, Diane admits her feelings, but explains that she is sacrificing their love to remain loyal to Richard. Although Diane tries to avoid Mike by starting her vacation with Richard early, Mike drops by their country house and, in spite of Diane's protests, vows to confront his rival. When Mike sees how kind and caring Richard is with Diane, however, he backs down from his threat and leaves abruptly. Afterward, Richard reveals to Diane that he had long sensed that she was in love with another man and nobly offers to divorce her. Unchained at last, Diane and Mike begin their married life on his Argentine ranch.