A calculating serial killer is poisoning victims in Edinburgh, engineering slow and painful deaths while remaining hidden. DI Luc Callanach and DCI Ava Turner are tasked with apprehending this elusive murderer, who derives pleasure from observing suffering from a distance. The killer's method involves administering undetectable poisons, leading to victims' unawareness until the drugs have irrevocably flooded their systems. This case presents Callanach and Turner with their most formidable challenge yet, as they grapple with the seemingly impossible task of catching a perpetrator who operates from the shadows.

This novel is presented as a gripping crime thriller with a relentless pace and clever plotting, characteristic of the DI Callanach series. Reviewers have praised the series for its detective work and intriguing premises, with specific mention of a sinister setup and a compelling killer's voice. The book is expected to deliver a high level of suspense as Callanach and Turner confront a particularly insidious and difficult-to-trace murderer. The reception suggests a strong entry in a well-regarded detective series, appealing to readers who enjoy intricate crime puzzles and psychological tension.