When Carmelita Lindsey threatens to divorce her husband Dennis on their first wedding anniversary because of his preoccupation with business, uncle Matt Lindsey decides to reconcile the quareling couple by bringing an infant into their lives. Consequently, Matt cables his friend, Lord Basil Epping, to arrange for Dennis and Carmelita to adopt a French war orphan. Lord Epping adopts an orphan from the wrong war, however, and arrives in New York with Fifi, a blonde French bombshell. To keep his new "daughter" secret from Carmelita, Dennis orders Matt to take Fifi out of town, and they hide out at the Bide A While Inn at Lake Cherokee. Soon after, Fifi's fiancée, Lieutenant Pierre Gaston de la Blanc, visits the Lindsey apartment in search of Fifi, leading Aunt Della to think that Carmelita is having an affair with him. After Pierre leaves, Aunt Della hears a radio broadcast from Lake Cherokee announcing that advertising executive Matt Lindsey is dancing with Fifi at the resort, and she insists upon immediately driving to the lake. Meanwhile, at the resort, Miss Pepper, the hotel manager, has become suspicious of Matt and Fifi's relationship and hides under Matt's bed to discover if he is an adulterer. Aunt Della, Carmelita, Dennis and Lord Epping then arrive at the lake, and after accusing Carmelita of adultery, Della bursts into Matt's room, where she finds Miss Pepper hiding under the bed. At that moment, Matt, who has been fixing a leaky faucet in Fifi's room, returns to his roo, and Della instructs Miss Pepper to call the police. When Della refuses to believe the truth about Fifi, Matt says that she is Lord Epping's fiancée, and Carmelita persuades Matt to pose as Epping and tell Della that he plans to divorce Lady Ada Epping. Lady Epping then arrives at the resort in search of her husband, and is greeted by Della who offers her sympathy. Marital woes abound when Carmelita overhears Fifi call Dennis "daddy," and she demands a divorce. Soon after, Pierre arrives at the hotel looking for Fifi, and Miss Pepper informs him that she has registered with Matt. Pierre declares that he intends to duel Matt for his honor, until he overhears Miss Pepper confide to the desk clerk that Lord Epping is divorcing his wife to marry Fifi. Matt, who has disguised himself as Lord Epping to hide from Pierre, is astonished when the Frenchman challenges him to a duel at dawn and Carmelita chooses knives as his weapon. As dawn approaches, Carmelita calls the sheriff to stop the duel. Before the sheriff can put on his jacket, Miss Pepper, who has observed Matt donning his Lord Epping disguise, phones and announces that Lord Epping is an impostor. The duel begins, and as Matt uses his sword as a bat to fend off Pierre's knives, the sheriff arrives. Miss Pepper then unmasks Matt, but when the real Lord Epping enters the hotel lobby, she faints.