Allergic to group activities, Serenata has run, swum, and cycled - on her lonesome. But now that she's hit 60, all that physical activity has destroyed her knees. As she contemplates surgery with dread, her previously sedentary husband chooses this precise moment to discover exercise. The story of an obsession, of a marriage, of a betrayal: Lionel Shriver at her hilarious, sharp-eyed, audacious best.