Series volume number provided by cataloger.

A particularly unpleasant murder, that of a very old woman in a housing project, rocks the town of Lafferton. The murderer has left a distinctive "sign" on the body and at the scene of crime. 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, tried but acquitted on the grounds of insufficient evidence.