When Jack Prescott's older, doting sister, Mabel, and her back-slapping jokester of a husband, Biff, show up unexpectedly and insist on meeting his fictitious fiancée, Jennifer, panic sets in. Fortunately for him, his neighbor, Valerie DiPietranitoni, arrives just in time to play that role. So well does she perform it that they decide to end the charade and try the real thing.