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 scandal…but 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…