Sometimes hope is the most dangerous thing of all.

When their brother dies, two sisters lose the one thing that connected them. But then a year after her twin's death, Tamsin goes missing.

Despite police indifference and her husband's doubts, Freya is determined to find her sister. But a trail of diary entries reveals a woman she barely knew, and a danger she can scarcely fathom, full of deep waters and shadowy myths, where the grief that drove Tamsin to the edge of a cliff also led her into the arms of a mysterious stranger ... A man who promised hope but demanded sacrifice...