Widely acknowledged as the first detective novel, this story is narrated by insurance investigator Ralph Henderson, who is building a case against the sinister Baron "R**", suspected of murdering his wife in order to obtain significant life insurance payments. Henderson descends into a maze of intrigue including a diabolical mesmerist, kidnapping by gypsies, slow-poisoners, a rich uncle's will and three murders. Presented in the form of diary entries, family letters, chemical analysis reports and interviews with witnesses, the novel displays innovative techniques that would not become common features of detective fiction until the 1920s.