Jim Buchanan, Herbert Marshall, is the wealthy president of Buchanan Motor Company, and his engagement to Evelyn Fletcher—a bossy socialite more interested in his money than in him—sets up a world where appearances matter as much as affection. When his colleagues reject his bold plan to roll out a new automobile design, he quietly chooses to step away from the pressure and take a vacation, hoping a change of scenery might clear his head and his ambitions.
While strolling in the park, he meets Joan Hawthorne, Jean Arthur, a young woman who has just been evicted and struggles to land a job. Thinking he too is job-hunting, she persuades him to pose as her husband so they can qualify for a joint application that would pair a butler and a cook. He agrees, and the pair quickly enters a playful, risky partnership that soon pulls them into a much larger scheme.
Under the alias "Mr. and Mrs. Burns," they are hired by Michael Rossini, [Leo Carrillo]. She proves to be a capable cook, while he uses the opportunity to study automobile sketches he once hid away in a safe, hoping to showcase his own design talents. He shares these sketches with Joan, who carries the designs to a rival executive. The man recognizes the distinctive style and, when Joan is later arrested for theft, she refuses to assist the police in finding Jim, all the while slowly falling for him.
Deciding to reveal himself, Jim plans to tell Joan his true identity. He writes a letter after she misses a lunch date, then abandons his masquerade for Evelyn and resumes life as a businessman. Meanwhile, Rossini has just organized a bootlegging operation and keeps tabs on Jim with the help of Flash, [Lionel Stander], who tails him and relays news to Rossini. Eager to win Joan, Rossini has her released from custody and explains Jim’s real identity, setting the stage for a confrontation that could end them both.
Joan’s initial anger shifts toward forgiveness as she recognizes her growing love for Jim, but Rossini wastes no time in making his move—he orders his henchmen to kill Jim at the wedding. He also tries to win Joan over by telling her the truth about Jim, yet she proclaims her love and pleads with him to spare Jim’s life. When Jim is seized at the altar, Rossini arrives with his gang and drags him home, insisting on a hurried ceremony with a justice of the peace to seal the marriage, while Joan resists and locks herself in her room.
To turn the tide, Jim leans into a calculated ruse: because Rossini’s men were seen taking him, the gang is coerced into cooperating with his plan. Outside Joan’s room, Rossini feigns a quarrel with Jim, and Flash fires a warning shot as Jim pretends to be struck down. The staged moment works—the sight of Jim “injured” and the looming wedding persuades Joan to come to his side, and the couple’s resolve to be together ultimately survives the perilous interference of Rossini’s gang.