A mystery bookstore blog post inspires a serial killer in Swanson’s Eight Perfect Murders (Morrow, Mar.).

How did you come up with the premise?

I was taking a walk around Walden Pond, and mentally trying to come up with a clever murder idea for another project I was thinking of doing. I began internally listing some of my favorite fictional murders to myself, and the idea for the book popped into my head. Not just the premise, but almost the entire book. By the end of my walk, I knew who the narrator was, who the killer was, and pretty much how the whole book would play out. That’s never happened before. It was exciting, but also overwhelming, because then I had to go home and try to write the thing.

Do the eight perfect murders in the book mirror your own choices for the eight best fictional murders, or did you choose them to better fit with the plot?

When I began to construct the list, I was thinking specifically of books that proposed clever ideas for murders, ideas that would baffle a detective. But I was also definitely looking for books that would work within the context of my plot. The A.B.C. Murders is definitely not my favorite Christie book—that would be And Then There Were None. But it wouldn’t make sense to have someone try and copycat that. They’d need a remote island and 10 victims—way too much work.

Any qualms about spoiling the endings of the eight perfect murders?

Hmm, a little bit, but not that much. The way I rationalized it was to say to myself that anyone who’s reading my book and hasn’t read Agatha Christie, or Patricia Highsmith, needs to get their priorities straight. Also, even though I do spoil many of the books I discuss, there are also many surprises in those books that I don’t spoil. Except for The Murder of Roger Ackroyd, which is, frankly, a one-surprise book.

Early on, you suggest that the narrator may not be 100% reliable. Can you discuss your thinking in sharing that at that point of the book?

I think what I wanted to do was to get ahead of the readers who would already be second-guessing the book in the early pages. It was a way to acknowledge the rules the narrator was establishing, but it was also a way for me to say, I already know what you’re thinking, and you might be right, and you might be wrong. And if readers weren’t already wondering about the reliability of the narrator, then it was a way of keeping them on their toes.