Friday the thirteenth of May was most unlucky day for Sergeant Caleb Martin of Kingsmarkham CID. That day he confiscated a replica gun from his son's school briefcase and lost his life in a bank robbery -- the first link in a chain of events which led to a series of deaths. When three people are discovered shot at Tancred House, Chief Inspector Wexford suspects a connection between the two apparently unrelated crimes. But only the seventeen-year-old daughter of one of the victims survives to provide the most confusing of clues. Although Wexford is very taken with the crime's only witness, Daisy Hoy, his feelings do not prevent his deductive powers from functioning with customary intuitive precision.