Bill Norman, an aspiring ichthyologist, exasperates his milk magnate father Rufus with his love of fish and his dreams of expensive scientific expeditions in the tropics. To keep Bill from absconding with his yacht, Rufus bets him that if he can work diligently as a milkman in the Norman dairy for one month, he will win the right to use the family yacht for a six-month cruise. On time every morning, Bill happily delivers milk to all of his customers, including Sheila Harrison, a pretty but impoverished debutante whom Bill believes is the Harrison maid. Although she is pursued by the rich and foppish Wally Martin, her mother's marital choice, Sheila sneaks off every night to date Bill, unaware of his upper class identity. When Rufus hears of his son's interest in a "serving" girl, he forces Bill to break a date with her and take his cousin Adele to a charity ball. The same day, Mrs. Harrison talks Sheila into going to the ball with the dejected Wally, who then is knocked out by a jealous Bill. At first jealous of Adele, Sheila eventually learns from milkman Hogan the truth about Bill, who has been jailed for climbing the Harrison house, and agrees to pose as him so that he will win his father's bet. Although Bill bails himself out of jail and joins up with Sheila in the milk truck, he is pursued by a fleet of policemen who believe that Sheila has been kidnapped. After a dangerous chase, Bill and Sheila arrive at the dairy in time to win the wager and be blessed by Rufus and Mrs. Harrison.