Hereby stand warned: In discussing mystery fiction in any sort of depth, including plot points and motivations, certain spoilers may arise that could affect a first-time readers’ enjoyment of the books under discussion. Proceed at your own risk.

The modern serial killer tale is typically a crime novel or procedural rather than a mystery, and the inner workings of the mind of the killer hold as much fascination for the authors and readers of those books as does the investigation into into the killer’s work. Often, the main “mystery” is the search for a link to connect the killings.

Agatha Christie was, first and foremost, a whodunit writer, and that element is always paramount in her books, be they detective novels or thrillers. The focus is on the detective’s investigation, and the revelation of the killers in the three books I discussed last week (And Then There Were None, Murder Is Easy and The Mousetrap) were all surprising and satisfactory. Christie rarely looks at the crimes from the point of view of the killer, and when this occurs, it is cleverly disguised to prevent giving away the ending. Only at the end of ATTWN do we get an extended look at the killer’s mind through a confession. Other examples, done briefly and brilliantly, occur in Toward Zero and After the Funeral. For a more major example you have only to look to . . . well, I’ll never tell!

With each visit into the world of the serial killer, Christie attempted something new. Perhaps she visited this plot point rarely because she never wanted to repeat the basic structure of this kind of story. The three examples I share today perhaps prove the wisdom of this thinking because each one is both unique and a gem.

     The A.B.C. Murders (1936), shows Christie once again experimenting with the form and rules of the traditional mystery.  Rather than a specific setting with a closed circle of suspects, Hercule Poirot sets upon a search throughout England for a serial killer whose modus operandi is frighteningly simple: the victims and the locations follow an alphabetical scheme, but essentially the crimes can happen anywhere and to anyone. Christie brings back Captain Arthur Hastings as narrator. (Out of thirty-three Poirot novels – if you count The Big Four as a novel – Hastings figures in eight of them. Arguably, this novel is the very best of the Hastings books.) Yet, even Hastings operates differently here, for he attempts, in alternating chapters, to create a second point of view, that of Alexander Bonaparte Cust, or A.B.C., a troubled war veteran whose path as a stocking salesman runs suspiciously parallel to our killer. Thus, to make matters worse for fans of traditional Christie, the killer seems to have been openly identified, making this feel like the prototype for the modern serial killer mystery, where the suspense lies in the capture, rather than the unmasking, of the culprit.

Christie pushes all the right buttons of her readers here: the fear that war veterans returning to England may be “not quite right,” the English sense of sticking together (the family members of the victims band into a group of sleuthing assistants to Poirot), and the suspense generated by a killer who is so insane that something as elementary as the alphabet inspires him to kill randomly. It’s as if all the rules of a traditional mystery – that sense that order can be restored after we play the game with Poirot – has been tossed out the window. Is it any wonder that some 1936 reviewers had to reassure readers that, with patience, they would soon find themselves comfortably ensconced back into a Golden Age detective novel?

The terror generated by a serial killer who could be anyone around you and who could, with a moderate degree of cleverness, escape capture comes through wonderfully in a sequence set during a horse race in Doncaster. In bright daylight, before a huge crowd of spectators, the six members of Poirot’s team try to pin down a killer before he strikes again. It all culminates in a chilling moment in a darkened movie theatre.The chapters showing the deterioration of Mr. Cust’s mental state are also beautifully rendered, and he remains one of Christie’s most beautifully pathetic characters.

If The A.B.C. Murders is ultimately a traditional mystery disguised as a serial killer hunt, The Pale Horse (1961) is also one kind of tale disguised as another. This is one of Christie’s strongest novels of her late period, and possesses another great Christie set-up: a dying woman hands a list of names to her priest and confesses that something evil is afoot. The priest himself dies soon after, but the list re-emerges, a list of people who have died, seemingly of natural causes. But what if the causes were not natural? What if the supernatural has played a hand in each death?

Christie had dabbled with the possible presence of occult elements in other novels, most notably with spirits in The Sittaford Mystery, and here she suggests that evil can be harnessed into a scheme to “kill-to-order.” Here she pulls out all the stops to convince readers that, maybe this time, witchcraft does have something to do with the terrible things going on. She adds to the strangeness by eliminating Poirot or Miss Marple from the scene and bringing on a new, untested amateur sleuth (although she does drop some wonderful cookies for her fans with cameos by a number of past characters, including Mrs. Oliver.)

But this is Christie, and nobody will be taken in for long that she has turned to writing a horror novel. The question then becomes who or what is behind this string of murders and how they are being accomplished. The solution is most satisfactory, and it sets this novel apart from most other Christie mysteries. It has the most satisfying revelation of a conspiracy and its mastermind since The Seven Dials Mystery, a solution that casts away all fears of supernatural agencies and places the actions and motivations firmly on this earthly plain . . . uncomfortably so, it would seem, for Christie uses her lifelong interest in the chemistry of poisons to come up with an all too real scenario for mass murder. In fact, the most frightening aspect of The Pale Horse is that it has served as inspiration for more than one real-life murderer!

However, although the motives for these killings are grounded in the stuff of traditional mystery, I would argue that the mastermind of this scheme is, without a doubt, a serial killer. There is a cold-blooded glee to this plan, a total disregard for human life and suffering, and in fact a sense of joy in killing and getting away with it. In this method lies madness.

Curtain, which was published at the end of Christie’s career but written decades earlier, serves as a swan song for Hercule Poirot. It is, in a way, the antithesis of The A.B.C. Murders. Poirot dedicates his failing energies to the pursuit and capture of what this time, without doubt, is a serial killer. This madman kills again and again, but his method of killing, which I will not reveal here, is utterly malevolent and unique amongst the Christie annals. Some very extraordinary things happen in this novel, but Christie sees to it that they are couched in traditional mystery terms, with a grand old mansion and a closed circle of suspects. She returns Captain Hastings to his place as narrator for the last time, and she brings us back to Styles Court, where Hastings and Poirot met in their first recorded adventure together. This only makes the series of revelations that follow more dramatic for the reader. The killer in this book most resembles those serial killers we find in modern novels: monstrous yet ordinary, willing to kill for reasons that most of us would never comprehend. And since the people staying in Styles Court are a fairly ordinary group, the reveal of one of them as a monster is devastating, made even more so by the ultimate effect it has on the lives of Poirot and Hastings. In no other novel can I remember a more certain sense of loss after the case is over than what Hastings must face as the curtain is drawn on his career as Poirot’s Watson.

The serial killer as culprit accounts for only a small percentage in Agatha Christie’s rogue’s gallery. Hopefully, this discussion has shown that her efforts to tell this sort of story, although not as graphic or centered on the mental state of the killer as those of Val McDermid or Bill Pronzini, are worthy of attention and admiration. If you are looking to read Christie in her entirety, I would space these out and savor them. If you are a long-time Christie fan, all six of these books are worthy of a second look.