The enigmatic and aristocratic Karen Knightly has recently broken up with her lover, whereas Henry Bell, a conventional middle-management type, has just lost his job. Their diametrically opposed worlds intersect one rainy night on Tower Bridge, because both of them have deciced to put an end to things in the muddy waters of the Thames. Yet on finfing Karen hanging from the bridge, Henry effects a clumsy but successful rescue. Once out of danger, they recount their misfortunes to each other. Driven by bittenness, their shared desire to do away with themselves is transformed into a desire for revenge at which point Karen decides to organize a dangerous game.