As newlyweds Gary and Geraldine Ainsworth celebrate their one month wedding anniversary, Gary's former sweetheart, Mabel Essington, phones to make arrangements to return a souvenir that Gary had given her while they were vacationing in Mexico City. Mabel's fiancé, Arthur Weldon, is also Gary's business partner, and consequently, when Mabel arrives at the office to return Gary's gift and Arthur announces that he has suddenly been called out of town on business, Gary offers to share a taxi with Mabel. On the ride home, Mabel returns the gift, a slip which turns out to be embroidered with the endearment "close to your heart, never apart, Love Gary." When Gary deliberately leaves the package in the cab, Mabel delivers it to his apartment and warns him that she will show it to Geraldine unless he tells his bride about their romance in Mexico. That weekend, Gary, Geraldine, Arthur and Mabel gather at the country home of Arthur's older sister Martha along with Alicia and Jimmy Larchmont. Suspicious of her husband's relationship with Mabel, Geraldine observes his behavior with vigilance while Gary bribes Boris, the waiter, to sneak into Mabel's room and steal the slip. After rifling through Mabel's suitcases, Boris finds the slip and delivers it to Gary, who furtively stuffs it into his dinner jacket. Victorious, Gary dances with Geraldine, but when the slip slides out of his jacket, he stuffs it into a vase and then smugly promises Mabel that when she produces the slip, he will tell Geraldine about their tryst in Mexico. Gary's victory is shortlived, however, as he discovers that Boris has stolen the wrong slip. Perturbed by her husband's odd behavior, Geraldine phones her domineering mother for advice. Alicia, meanwhile, becomes annoyed by Geraldine's immaturity, and decides to teach her a lesson by flirting with Gary. When Gary confides about his "slip" to the solicitous Alicia, Alicia misunderstands and thinks that he has fathered an illegitimate child. Upon discovering that her room has been searched, Mabel tells Martha about the slip and her Mexico City rendezvous with Gary. Determined to recover the slip, Boris and Gary climb onto the roof and into Mabel's bedroom window, but when Mabel enters the room, they are forced to crawl under the bed. Geraldine reports seeing a man on the roof, and Martha grabs her shotgun and goes to look for the intruder. Meanwhile, Jimmy becomes jealous of his wife's attention to Gary, and accuses her of having an affair. After Mabel leaves her bedroom for her dressing room, Boris discovers the slip and hands it to Gary. At that moment, Jimmy bursts into the room and thinks that Gary is holding Alicia's slip. When Arthur knocks at the door to speak to Mabel, Jimmy, Boris and Gary seek refuge under the bed. After Mabel returns to her room and discovers the men hiding under her bed, Boris climbs onto the roof and Martha shoots at him, sending him scurrying back through the window. Martha then runs back into the house to warn of the intruder, causing Geraldine to faint. From her prone position on the floor, Geraldine spies her husband hiding under Mabel's bed. Ostracized by all for his alleged romantic exploits, Gary is seated alone in the library the next morning when Martha enters carrying the baby of her maid's sister. Explaining that Priscilla, her maid, is to be married that morning, Martha asks Gary to watch the baby while she attends the wedding and then assures him that she has disposed of the incriminating slip by giving it to Priscilla as a wedding gift. After Martha leaves the house, Alicia and Arthur see Gary holding the infant and assume that it his illegitimate child. When they refuse to believe Mabel's story about the slip, Boris and Gary hurry to the wedding to retrieve it. After interrupting the ceremony, Boris tries to remove the slip from Priscilla, causing the groom to slug both Boris and Gary. Back at the house, meanwhile, Geraldine is about to depart when Gary returns bearing the slip. Contrite, Arthur apologizes to Mabel, and when Geraldine's mother phones to give her daughter advice, Geraldine, now secure in her marriage, refuses to take her call.