"FBI forensic linguist Raisa Susanto thinks she's through with the past now that her psychopathic serial killer sister, Isabel, is locked away forever. Then Raisa receives a letter from Isabel. It's just a single message: By the time you read this, I'll be dead. Soon after, Isabel is discovered dead in her cell, forcing Raisa back into her depraved orbit -- one that includes a band of true-crime worshippers obsessed with Isabel, her killing spree, and those who survived it. When a new victim is killed in the same manner that made Isabel notorious, Raisa and FBI forensic psychologist Callum Kilkenny aren't just tasked with finding out who killed Isabel and why. They're hunting for a protégé following in Isabel's footsteps. Raisa must uncover the truth -- whether or not she's ready for it -- before someone else dies.