Former FBI agent Sam Delvecchio's first assignment for missing person's unit The Mercy Street Foundation has all the telltale signs of a serial killer's work. And his grim suspicion is confirmed when agent Fiona Summers shares the details of two other killings with eerie similarities. When a fourth victim is then discovered, it's obvious that they're pursuing the same twisted quarry. Then Sam and Fiona realise the killer's horrific intent - the staging of the Catholic Church's seven Acts of Mercy with the bodies of his victims. But it's not until they are both racing to prevent the final three murders, and they start receiving taunting messages from their target, that the terror really begins ...