The Retreat (Broché)

An idyllic wellness retreat has opened on an island off the coast of Devon, promising rest and relaxation - but the island itself, known locally as Reaper's Rock, has a dark past. Once the playground of a serial killer, it's rumoured to be cursed. A woman is fund dead below the yoga pavilion in what seems to be a tragic fall. But DS Elin Warner soon learns that the victim wasn't a guest - she wasn't meant to be on the island at all.
The longer Elio stays, the more secrets sise uncovers. And when someone else drowns in a diving incident, Elin begins to suspect that the old stories about the island are true.