The search for a missing journalist is called off as a body is found at the scene of a carefully staged murder. In a sealed chamber, deep in the heart of Gilmerton Cove, a mysterious network of caves and passages sprawling beneath Edinburgh, the victim has undergone a macabre ritual of purification. Inspector Tony McLean knew the dead man, and can't shake off the suspicion that there is far more to this case than meets the eye. The baffling lack of forensics at the crime scene seems impossible. But it is not the only thing about this case that McLean will find beyond belief. Teamed with the most unlikely and unwelcome of allies, he must track down a killer driven by the darkest compulsions, who will answer only to a higher power...