A psychology student researches infidelity by becoming a platonic kept woman for four buddies.

Bachelor Fred Williams and his three married friends, George, Doug, and Howard, are Manhattan commuters from Connecticut who decide to rent an apartment in New York City and furnish it with a beautiful blonde to be available to each of them on different nights of the week. In answer to a New York Times advertisement, Cathy, an attractive young woman, accepts the position. Unknown to the "boys," she is actually a sociology student preparing a thesis on the sexual patterns of the suburban male. By clever maneuvering, she manages to subdue their amorous intentions. Although their evenings with Cathy are completely innocent, the three married men lie to Fred about their torrid evenings at the apartment. Wildly jealous, he proposes to Cathy, and she accepts. Meanwhile, the three wives have learned of the situation through a private investigator, and they arrive at the apartment in a rage. All misunderstandings are cleared up, however, when Cathy reveals her true motive for accepting the housekeeper job. Furious at having been duped, Fred walks out, but the wives, aided by Fred's mother, promptly drag him back. He decides to become the fourth member of a quartet of husbands who spend a weekly night on the town--with their wives.