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The "whydunnit"— what would prompt someone to betray their country? — is more intriguing than the "whodunnit," but not by much because "All the Old Knives" does not provide enough backstory.

The Guardian called it ”a fantastically compelling, brilliantly scripted whydunnit.”

Ms. Greene called the novel “not so much a whodunnit as a whydunnit,” inspired by a similar 1984 murder in Bangor, Maine.

At the moment we’re just following the narrative of the murderer; it’s a whodunnit rather than a whydunnit.”

That’s the arresting beginning of Christopher J. Yates’s “Grist Mill Road,” a whydunnit that delves deep into the secrets linking the main characters in this macabre vignette: Hannah, the victim; Matthew, the teenager with the gun; and Patrick, another boy who is present but does not intervene.