A 24-year-old divorcee, Betty Preisser, a receptionist for a clothing manufacturer, takes some office work home which her boss, widower Jerry Kingsley, a man of 56, drops by to pick up. Professional rather than personal acquaintances, Betty tells Jerry of her loveless marriage to George, a musician. Jerry has a married daughter, Lillian, about her age, and a spinster sister, Evelyn, who is very protective of him.
Jerry works up the nerve to invite Betty to dinner. He meets Betty's mother, Mrs. Mueller, and sister Alice, who share the apartment with Betty. Their relationship grows, but she professes to be reluctant to date her employer. Jerry wonders if their age difference is really behind this reluctance. Despite this, a May–December relationship between them develops.
Female family members of both of them strongly disapprove. Mrs. Mueller calls him a "dirty old man," while Jerry's sister calls Betty a "fortune hunter" and him a fool, although Lillian's husband Jack offers his congratulations, earning scorn from his wife and causing them to quarrel. A colleague, Walter Lockman, trapped in a long and unhappy marriage, urges Jerry to do whatever it takes to find true happiness.
George returns to town and tries to persuade Betty to return to him. In a moment of weakness, they have a romantic tryst. Betty regrets it and explains to Jerry that it meant nothing to her emotionally, but he feels humiliated. His sister observes how depressed Jerry has become when he returns home. At his lowest ebb, he learns that Walter has taken an overdose of pills in a likely suicide attempt. Jerry sees it as a sign to seize the joy in life while he still can. He returns to Betty's waiting arms.