Overworked parents Tacey (Maureen O'Hara) and Harry King (Robert Young) have three rambunctious sons and no time for themselves. So they place an ad for a live-in nanny, which is answered by one Lynn Belvedere, who they assume is a woman. The Kings are soon shocked when they discover that Lynn is actually a man (Clifton Webb). Reluctantly, they hire him anyway and are pleased when he proves a success. Unfortunately, the addition of another adult man to the house troubles the neighbors.