Unknown to DI Luc Callanach and the newly promoted DCI Ava Turner, a serial killer has Edinburgh firmly in his grip. The killer is taking his victims in the coldest, most calculating way possible - engineering slow and painful deaths by poison, with his victims entirely unaware of the drugs flooding their bloodstream until it's too late. But how do you catch a killer who hides in the shadows? Perfect for fans of Karin Slaughter and M.J. Arlidge.