Walter Matthau stars as Julian Winston, an easygoing bachelor dentist whose delicately balanced scheme to get married crumbles under some unexpected circumstances. Winston is stringing along his dizzy blonde mistress, Toni (Goldie Hawn), by telling her that he has a wife and children. But when he learns that she has tried to commit suicide over him, he promises to marry her. Toni, refusing to be a home wrecker, insists on first meeting Winston's wife, so he convinces Stephanie (Ingrid Bergman) -- his starched and no-nonsense nurse -- to pose as his wife. Winston's scheme leads to unforeseen twists and surprises for everyone.