1863. Superintendent Henry Jarrett, chief of the detective department at Glasgow Central, is under pressure from the Union Bank who are in the midst of a forgery scandalbut just as that investigation gets under way, the murders begin. Although there is no particular modus operandi, each killing is claimed by a letter-writer calling himself the Scythe. This mysterious character paints himself as a righter of wrongs and is seemingly in possession of facts known only to the detectives. But what troubles Jarrett most apart from the fact that the lady in his life seems to be taking too great an interest in a dashing sea captain is that the most recent murder is not accompanied by the usual letter. Now it seems that Jarrett has two killers to contend with