Clem gets a call that is every mother’s worst nightmare. Her 19-year-old daughter, Erin, is unconscious in the hospital after a hiking trip with her friends on the remote Orkney Islands that met a horrifying end, leaving her boyfriend dead and her best friend missing. When Erin wakes, she doesn’t recognize her mother. And she doesn’t answer to her name but insists she is someone named Nyx. Clem travels the site of her daughter’s accident, determined to find out what happened to her. The answer may lie in a dark secret in the history of the Orkneys: a woman wrongly accused of witchcraft and murder four centuries ago. Clem begins to wonder if Erin’s strange behavior is a symptom of a broken mind or the effects of an ancient curse.

On a small Greek island, a woman comes ashore with no memory of who she is, where she's from, or how she came to be shipwrecked there. As she's nursed back to health by the island's only inhabitants, four friends on an annual retreat, she detects tensions between the group that suggest not all is quite as it seems. Her new acquaintances each appear to be hiding something --- something that may relate to the mystery of her identity. Meanwhile, in a pretty suburb on the outskirts of London, Eloise vanishes into thin air. Her husband, Lochlan, is desperate to find her --- but as the police look into the disappearance, it becomes clear that Lochlan and Eloise's marriage was not the perfect union it appeared.