James Croxley is a successful picture-restorer. His wife Eleanor sings in a choir which is to perform Bach's St Matthew Passion at the Albert Hall. Together, they have shared twenty-five happily married years, faithful, fulfilled - and boring. So when Kate, mistress of the late Albert (a close friend of James) and accomplished marriage-wrecker, appears on the scene James easily falls prey to a banal affair with this young seductress, despite his love for Eleanor and the full awareness of the destructive nature of his actions. Hungry for revenge on Kate, Agnes, widow of Albert, informs Eleanor of the affair between Kate and James. There follows a searing examination of the disruption and hurt caused by marital infidelity with the introduction of alter-egos for James and Eleanor - Jim and Nell - acting as the couple's conscience, commenting on their actions and the pretences they must now adopt as a survival tactic