In Casebook, Simpson’s latest novel, adolescent Miles Adler-Hart watches his newly divorced mathematician mother, Irene, fall in love with a man named Eli Lee. Miles takes his interest in spying to an entirely new level as he investigates Eli’s past. Set in Santa Monica, the novel is an intimate look at a love affair with a charming man who rarely tells the truth.

What books did you read as you wrote Casebook?

I read a lot of books about psychopaths. I read a wonderful book Amy Hempel gave me about the guy who created criminal profiling—a fascinating book. Mind Hunter. I read a bunch of books about math, a number of books about lying and all of that. Letters to a Young Mathematician, a few books on cartooning. A bunch of graphic novels. Sherlock Holmes.

Did you always know Miles would tell this story?

I very much thought about Irene’s and Eli’s points of view. I felt like I needed the limitation, you might say—the restrained access that Miles had.

Why did you make Irene a mathematician?

I somehow saw her as a contained person, a very logical, rational, clean-angled sort of mind. I wanted to see how a real rationalist, in a way, would fall in love. I read a lot of books, but I also talked to a number of mathematicians. I also wanted to talk to women who are mathematicians, because it is still one of those fields which is predominately male.

Readers rarely see the given names of Miles’s mother or sisters—instead they are referred to by their nicknames, “the Mims” and “the Boops.” What made you decide to do that?

I wanted it to sort of have a personal feeling, a personal, affectionate feeling. I wanted the reader to feel a little bit inside this family.

Could you talk about the role animals play in this novel?

I wanted something that would come from Eli that would become adopted by someone in the family, a tangential thing that didn’t pertain to his central purpose there. The more you learn about animals and animal rights—it’s an intriguing, fascinating world. I was in a book group a few years ago with two veterinarians. One who collected strays in downtown L.A. at night—he had a van and would go and collect all the homeless pit bulls. [The other vet] worked with rescued exotics.

There are brief references to Hollywood—mostly related to Miles’s father’s job—but the industry doesn’t play a major role. What effect did you want its presence to have?

This novel is very much my attempt at a love story. It’s not primarily about the divorce—it’s a little bit about the divorce. I wanted the pattern to follow the national normal trend—apparently, after divorce, the women and kids usually end up poor. I wanted that to be a little bit in the background.

The novel includes a few illustrations. When and how did you decide you wanted to include these?

I always wanted to do illustrations—the sad thing is, I tried to do them myself. (Laughs). I took a few lessons and got a sketchbook and I sent in my sketches…everyone agreed that they were not quite ready. I hired [someone].

Miles has such a kind heart. In earlier drafts, did he have a meaner side?

In general, this is my attempt at a love story, but in many ways it’s a friendship story. [Friendship] includes some meanness, some competition, some envy—a constant awareness of who’s up and who’s down, who’s getting what and who’s not getting what…I wanted the friendship to be a sustaining banister in both their youths.

Did you know the whole time how your story would end?

I knew, pretty much. It’s a different thing to write a love story now than in the time of Jane Austen, Eliot, or Tolstoy. One of the problems is that once divorce is possible, once break-ups are possible, it can all become a little less momentous. One is always thinking: what are the real life stakes here? What, really, has a person lost? I wanted to have some real stakes.

Miles hires a private investigator, Ben Orion, who is a markedly different character from Irene’s pool of academic friends. They become quite close nonetheless. Did you go to a different place in your mind as you created him?

I guess so. I like him—he’s sort of a favorite of mine. He came out of a little bit of research—I did interview a few detectives. I think that’s one of the interesting things about romantic love —it’s really interesting when it includes big differences. Racial difference, cultural difference, any of those things.

Sometimes you seem to mock this family’s liberalism affectionately. Do you think this family tries too hard to be politically correct? Is this just pure earnestness at its best?

I both mock it but I wouldn’t want it any other way. We’re all looking for an authentic way to be engaged in the community, engaged in politics, engaged in national discussion—and so, we’re clunky. We’re all clunky. But it’s better than not doing it.