Andrew (Woody Allen), an eccentric inventor, joins his wife, Adrian (Mary Steenburgen), for a weekend at the New England country estate of her cousin, Leopold (Jose Ferrer), a wealthy charmer. They are soon joined by a playboy physician (Tony Roberts) and his spirited younger girlfriend (Julie Hagerty). As the long summer weekend wears on, sexual sparks begin to fly between Andrew and Leopold's young fiancée, Ariel (Mia Farrow), with unforeseen consequences for everyone.