C.C. Baxter (Jack Lemmon), a dedicated and ambitious insurance clerk, lends his Upper West Side apartment to company executives for their secret liaisons in hopes of climbing the corporate ladder. His plan seems to work when his boss, Mr. Sheldrake (Fred MacMurray), promises him a promotion in exchange for the key to the apartment. However, Baxter’s aspirations shake when he discovers that Sheldrake’s mistress is Fran Kubelik (Shirley MacLaine), the kind and charming elevator operator Baxter has fallen for. As Kubelik’s relationship with Sheldrake becomes more complicated, Baxter faces a moral dilemma: should he continue to allow his apartment to be used for Sheldrake’s trysts, or should he stand up for his own values and pursue a genuine relationship with Kubelik? The choice Baxter makes will ultimately define his character and his future.