C.C. "Bud" Baxter (Jack Lemmon) knows the way to success in business... it's through the door of his apartment! By providing a perfect hideaway for philandering bosses, the ambitious young employee reaps a series of underserved promotions. But when Bud lends the key to big boss J.D. Sheldrake (Fred MacMurray), he not only advances his career, but his own love life as well. For Sheldrake's mistress is the lovely Fran Kubelik (Shirley MacLaine), elevator girl and angel of Bud's dreams. Convinced that he is the only man for Fran, Bud must make the most important executive decision of his career: lose the girl... or his job.