For those of us who have long wondered what is going on in the unusual brain of the British thriller writer Sophie Hannah, her entertaining recent work of nonfiction, “How to Hold a Grudge,” is a perfect document. It explains, among other things, her relish for parsing human motivation down to the subatomic level and her characters’ tendency to respond to normal events with abnormal behavior that holds some internal logic for them (and for her, since she made it up) but seems wackadoodle to the rest of us.

Now all is clear. It makes sense that a woman who would devote several pages to the litany of emotions she felt about a seemingly innocuous incident involving a friend and his dog would also be the author of “The Next to Die,” the latest in a series featuring the chronically dysfunctional, always amusing Culver Valley police officers.

This time around, they are forced to participate in a regional task force with officers from other jurisdictions. They’re looking for a serial killer who has murdered two pairs of best friends after sending them homemade white books containing snippets of foreboding poetry. (Pay attention to the use of books and stories in this plot.)

[ Read Sophie Hannah’s By the Book. ]

It’s a weird case, but these are weird cops. They begin their discussions by debating whether the name they have awarded the killer for publicity purposes — Billy Dead Mates, a play on “Billy No Mates,” Brit-speak for a person with no friends — even makes sense. “He’s killing pairs of best friends, yes, but they’re friends with each other, not with him,” one of the officers says. “To call him Billy Dead Mates implies he’s killing his own friends. And we’ve no reason to think he is.”