After he criticises police procedure in the aftermath of a murderer's capture, DS Sean Stone's superiors want him out of the way, so they assign him to a new 'unit' at the MPB with analyst Ruth Hattersley. However, the case of a vanished 16-year-old girl soon has the unorthodox detective back out in the field with his new partner. Looking into a spate of teen suicides, he believes he has discovered a killer preying on vulnerable youngsters.

While investigating the disappearance of 16-year-old Taylor, Sean discovers she was a member of an online social network linked to several suspected suicides. He believes a serial killer is posing as a teenage girl to prey on vulnerable youths, making each of them look like they have taken their own lives. Using his unique pattern-reading intelligence to figure out the murderer's method, the detective's net closes in - leading to a startling discovery.

Sean looks into the case of Stephen Eli, a lawyer and single father who fits none of the five most common categories of missing persons. Investigating his last known movements, the detective spots a connection with two deaths at the hands of murderer Leonard Vance, who is now incarcerated in a secure psychiatric hospital, and believes Stephen could be Vance's third victim.

The only thing Sean loves more than finding a pattern linking several people is discovering someone who doesn't fit it, so he's thrilled when he realises that missing lawyer and single father Stephen Eli is one such case. He believes Eli is a victim of imprisoned serial killer Vance, who eventually confesses to the crime. But when Vance can't guide police to Eli's body, Sean begins to wonder if he's made a mistake, and that somebody else is responsible for not only Eli's death, but also the other murders supposedly committed by Vance.