Summer and Iris are identical twins – asymmetrically, so when Iris looks at her sister, she sees her own reflection. But where Summer has succeeded – handsome husband, loving friends, immense wealth – Iris has failed, with one broken marriage already behind her and only jealousy to fuel her.

So when Summer asks Iris for a favour – to sail the family yacht out of a sticky situation in Thailand with her husband, Adam – Iris can see a future on the open sea, with a handsome man and a new way of wresting her father’s conditional inheritance from her siblings. But one morning, in the middle of the ocean, Iris wakes to find herself completely alone. It’s a struggle to get back to land, but on the arduous journey there, wracked with horror and grief, a new path appears before her. Can she take it? Can she sell it? And what will it cost?

This book has everything: a beautiful yacht; first-class living; endless, treacherous water; an inheritance that has seen a family discreetly torn into bitter pieces; a good twin and a bad twin. It’s a story laced with surprises and deceit; Carlyle, a sailor herself, knows her boats (I assume – I happily know nothing but love to read about them), and knows how to navigate readers through an excellent, twisty book and to drop anchor hard in an ending that will stop your heart.

Fiona Hardy is our monthly crime fiction columnist, and also blogs about children’s books at Fiona The Hardy.