My husband's lover. They said her death was a tragic accident. And I believed them . . . until now.

Carmen is happily married to Tom, a successful London lawyer and divorce with three children. She is content to absorb the stresses of being a stepmother to teenagers and the stain of 'second wife'. She knows she'll always live in the shadow of another woman - not Tom's first wife Laura, who is resolutely polite and determinedly respectable, but the lover that ended his first marriage: Zena. Zena who was shockingly beautiful. Zena who drowned swimming late one night.

But Carmen can overlook her husband's dead mistress . . . until she starts to suspect that he might have been the person who killed her.

'Absolutely gripping, I raced through Undertow at the speed of knots' Rosamund Lupton.