After 10 years, Guy--a drifter with a taste for deception--has returned to Coniston in England's Lake District. A local journalist, Tony di Venuto, is campaigning to revive interest in the disappearance of Emma Bestwick, and Guy knows what happened to her.
When he tips off the newspaperman that Emma will not be coming home, DCI Hannah Scarlett, head of Cumbria's Cold Case Review Team, re-opens the old investigation. Her enquiries take her to the Museum of Myth and Legend and to the remote and eerie Arsenic Labyrinth--a series of stone tunnels used to remove arsenic from tin ore.

Meanwhile, historian Daniel Kind is immersing himself in the work of John Ruskin, whose neighbors created the Arsenic Labyrinth. A shocking discovery makes it clear to Hannah that there is not one mystery to solve, but two, and she turns to Daniel for help in untangling the secrets of the past. As Hannah and Daniel struggle to resist a growing but dangerous attraction, Guy's plan to make a quick buck runs into trouble, and he has to resort to desperate measures. Someone is determined to kill to keep their secrets safe.
Set against the stunning backdrop of the Lake District in winter, the novel depicts how passionate relationships can lead to obsession and murder.