When Simon Serrailler is called in by Lafferton’s new Chief Constable, he is met by two plainclothes officers who ask him to take the principal role in a difficult, potentially dangerous undercover operation. He must leave town immediately, without telling anyone --- not even his girlfriend Rachel, who has only just moved in with him. To complete his special operation, Simon must inhabit the mind of the worst kind of criminal. This takes its toll on him and --- as the investigation unfolds --- also on the town and some of its most respected citizens.

The murder of a very old woman in a housing project rocks the town of Lafferton. A couple of weeks later, a similar murder occurs, and a month or so later, so does another. Initial investigations discover that the mysterious "sign" left on the body was the calling card of a suspect who was charged with several murders in the northwest of the country but was ultimately acquitted. All indications suggest that this person has simply vanished. Or is he right under their noses?