Roger Bradley, son of a milk magnate, isn't allowed to work for his dad's company because of a lingering war trauma: in moments of stress he quacks like a duck. Desperate to escape from idleness, he gets a job with his father's arch-rival, sponsored by eccentric milkman Breezy Albright, and promptly falls in love with the boss's daughter. But his career as a milkman soon degenerates into slapstick.

At the Club Nocturne, bumbling Roger Bradley and his date, Ginger Barton, are caught in a revolving door with gangster Mike Morrell. Just as things get straightened out, Roger sees what he believes is a runaway, driverless milk truck. Actually, the truck belongs to milkman Breezy Albright, an old friend of Roger's. Breezy explains to Roger and Ginger that he adapted the principle of an electric eye for use with sound and now controls his truck with a whistle. The next day, Roger tells his father, the owner of Bradley's Milk Company, that he wants a job. His father, however, does not believe that Roger has recovered from a traumatic accident during the war that causes him to quack like a duck when he is excited. The discouraged Roger then begs Breezy to help him get a job at the rival Happy Day milk company. Happy Day has been losing business to Bradley, and D. A. Abbott, the company's owner, blames manager John Carter, the nephew of major stockholder, Mrs. Laura Carter, for the situation. On Breezy's recommendation, Roger, pretending to be unrelated to the milk company Bradleys, is accepted as a milkman trainee. He is immediately smitten with Chris, Abbott's daughter, and tries very hard to become an outstanding milkman like Breezy. When Roger finally has a chance to go out on a route, however, he alienates all his customers, many of whom switch their accounts to Bradley. One day, while on a date in Buttermilk Lane, Roger and Chris have a chance encounter with Breezy and Ginger. Ginger innocently reveals Roger's real identity, and Chris, who has been keeping Roger's mistakes from her father, runs away. Meanwhile, Morrell confronts Carter, and demands that he steal his aunt's expensive necklace to pay his gambling debts. Carter places the stolen necklace in a bottle of milk and gives it to Roger to deliver to Morrell. Concerned about Roger's mistakes, Breezy follows him on his route. At Morrell's hotel, Roger demands eleven cents in payment for the milk, and when neither Morrell or his men can pay, refuses to hand over the milk. On his way out, Roger mistakenly assumes that the hotel is on fire and calls the fire department. In the ensuing confusion, a photographer snaps a picture and Breezy blocks his view of Roger. The photograph is published in the paper and Breezy is fired, four days short of the time needed for him to receive his pension. Later, Mrs. Carter, who has discovered that her necklace is missing, confronts Carter and threatens to turn him in to the police. In the meantime, Roger has learned that Breezy has lost his job, and rushes to the Carter residence to tell Mrs. Carter the truth. While he is there, Carter shoots his aunt from behind a curtain. Roger tries unsuccessfully to stop him and in the process, notices a snake ring on the gunman's finger. Although Mrs. Carter is only wounded, she is unable to name her attacker. Back at the milk company, Roger accidentally breaks the bottle containing Mrs. Carter's necklace and this eventually helps him identify Carter as the gunman. Then Morrell and his men arrive at the milk company, and Carter tries to escape in Breezy's truck. Breezy stops it with a whistle, and Carter and the gangsters are brought to justice. Later, Abbott and Bradley decide to merge their companies, while Chris and Roger, who is now totally cured of his quacking, plan their wedding, and Breezy gets his pension after all.