 Tacey and Harry King are a suburban couple with three sons and a serious need of a babysitter. Tacey puts an ad in the paper for a live-in babysitter, and the ad is answered by Lynn Belvedere. But when she arrives, she turns out to be a man. And not just any man, but a most eccentric, outrageously forthright genius with seemingly a million careers and experiences behind him. Mr. Belvedere works miracles with the children and the house but the Kings have no idea just what he s doing wit his evenings off. And when Harry has to go out of town on a business trip, a nosey parker starts a few ugly rumors. But everything comes out all right in the end thanks to Mr. Belvedere.