 A British yuppie couple have a presumably idyllic existence. Yet there is one troubling factor in their lives - an eccentric, and possibly, difficult mother-in-law (Diana Rigg). Her odd behavior is confirmed in a series of incidents involving her ex-husband (David McCallum), a concert musician, and her ex-husband s new wife, an artist. Flashbacks reveal bits of her troubled past. Little by little, the young couple s life begins to fall apart and the mother-in-law begins to act out her feelings of intense jealousy in the form of revenge, implicating a dear old friend, and leading to murder.