Tied to a derelict pier on Orkney, the bloated remains of a man bob in the waves, under the shadow of forbidding Sandisquoy House. The locals know him as William Spencer.
But DCI Lukas Mahler identifies him as Alex Fleming - his former boss.
Unable to step away from the case, Mahler tries to piece together why Fleming would retire to such a remote location. But the deeper he digs, the more disturbing the investigation becomes.
Seal bones, witches' salve, and runic symbols appear everywhere he looks, ushering Mahler towards Fleming's most notorious unsolved case: the 'Witchfinder' murders. And towards a dark and uncomfortable truth someone has gone to great lengths to bury...