The Eighth Detective by Alex Pavesi
Friday, August 21, 2020 at 7:12AM 
Published by Henry Holt and Co. on August 4, 2020
What defines a murder mystery? The Eighth Detective explores that question, and even provides examples of the definition’s permutations, in a plot that seems to be one thing and turns out to be something quite different.
Before his retirement, Grant McAllister was a professor of mathematics at the University of Edinburgh. A fan of murder mysteries, McAllister authored a paper in 1937 that purports to define the mathematical structure of murder mysteries in all their variations. To illustrate some of the key principles of his definition, McAllister wrote seven stories. In the 1940s, he collected the stories and the paper in a self-published volume called The White Murders.
The reader is told that the long-forgotten volume came into the hands of a small press publisher who thought it deserved an audience. He dispatches an editor, Julie Hart, to track down McAllister, who seems to have isolated himself on a Mediterranean island. Hart discusses the stories and the mathematical paper with McAllister in a series of interviews.
The Eighth Detective opens with the first short story that appears in The White Murders. The next chapter relates Hart’s discussion of the story with McAllister. The book then alternates short stories with discussions until it reaches the final discussion, in which Hart reveals the solution to a separate mystery that she has uncovered.
Alex Pavesi scores points for inventing such a clever concept. The stories are ordinary murder mysteries, some better than others. None are particularly impressive but none are unworthy of publication. As Hart reads them to McAllister, she spotlights inconsistencies in the text and wonders whether they are deliberate. McAllister’s answers are vague. At the novel’s end, we learn that we have been deceived about the stories in a way that I won’t spoil. The deception is critical to the plot and to a full understanding of the stories themselves.
The math in the research paper that Hart finds so complex consists of nothing more than Venn diagrams. McAllister defines every murder mystery in terms of four ingredients. With one exception, a story that lacks any of those ingredients is not a true murder mystery. Unsurprisingly, a murder mystery requires at least one murder victim, at least one killer, at least two suspects, and typically (but not inevitably) someone who solves the crime. The categories overlap, so that (for example) the detective or the victim might also be the murderer. McAllister also believes that the main structural variations of mystery stories can be broken down into archetypes. The stories are meant to illustrate seven of those.
Murder mysteries often depend on surprise endings (in many, the killer is the person we least suspect), a convention that, Hart opines, has carried over into the broader crime novel genre, even as traditional murder mysteries have diminished in popularity. The Eighth Detective follows that convention by serving up a couple of surprise endings. One changes the reader’s understanding of Hart (just as Hart changes the reader’s understanding of McAllister), while the other wraps up some dangling clues to an unsolved crime that Hart discovers in The White Murders.
Cleverness is its own reward in crime fiction. If The Eighth Detective didn’t blow me away, and if the “mathematical” analysis of murder mysteries seems a bit simplistic, those faults are easily overshadowed by Pavesi’s careful attention to storytelling details that create, in the end, an inventive novel that is both a murder mystery and a different kind of mystery — the story of two protagonists who each endeavor to keep secrets from the other for reasons of their own.
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