When a delivery driver stumbles across the dead body of a reclusive author in a remote area within a stone's throw of the Llyn Brianne dam, his first thoughts are that the elderly man has had a heart attack. But the knife sticking out of the corpse's chest tells a different story. Dial in some missing walkers, a secretive cult, and the unwelcome presence of paranormal-hunting podcasters and DCI Warlow has his work cut out getting to the rotten heart of the case.