Cactus Flower

Walter Matthau stars as Julian Winston, an easy-going bachelor dentist whose delicately balanced scheme crumbles under some unexpected circumstances. Winston is stringing along his dizzy blonde mistress, Toni (Goldie Hawn), by telling her he has a wife and children. When he learns that Toni has tried to commit suicide over him, however, he promises to marry her. Toni, refusing to be a homewrecker, insists on meeting Winston's wife. He convinces Stephanie (Bergman)--his starched, no-nonsense receptionist--to pose as his wife, and there are unforeseen twists and surprises for everyone. (official distributor synopsis)