It’s hard not to have heard of Dexter, what with the very popular television show. I don’t mind the show; it’s one of the two or three things I actually watch on the TV. For the time being, though, let’s pretend it doesn’t exist, because I want to talk about why Jeff Lindsay’s Dexter novels are some of my absolute favorite books off of the “mystery/thriller” shelf. (If you’re curious, I also deeply enjoy Gillian Flynn and Chelsea Cain, and you may spy a pattern there.)

But they’re not purely mystery, by my standards, and that’s been one of the best narrative surprises. The construction of the Dark Passenger, especially the depths of which Lindsay explores in the third book, strikes me as… Well, as Dexter might say, secretly speculative. (The alliteration and lyrical games in these books make them a treat for writers, by the way.)

It would be safe to say that mystery novels about psychic detectives, for example, have a certain level of the speculative. Ditto your ghost-whisperers, magical tattoo artists, and all the other sorts who show up in the cozies. They’re still mystery novels at their heart, and so are the Dexter books, but there’s something else lurking in there, too, in the form of Dexter’s inner guide and monster-friend.

I can’t decide if I’d call the Dark Passenger (or, as Cody refers to his own, Shadow Guy) a science fictional concept or a fantastical concept. It’s described in the third book in very evolutional, scientific terms: these things that have grown up out of people are no longer people, really, and they hunt the regular types—brought on by trauma, generally, but it’s the trauma that opens a door. The Dark Passenger in its reptilian, winged, hissing and chuckling glory is what comes through.

So—it’s definitely speculative. The way Lindsay writes the Passenger wouldn’t necessarily be so if it was limited to Dexter’s internal psychosis. He could imagine anything he wanted; it could be his way of describing the urges he feels as a serial killer. However: every predator in the series with a touch of the Passenger reacts the same way and contains the same Other. They can recognize each other by the rustle of wings and the contact of eyes. If it worked that way in real life, well, I don’t know: would we have more serial killers, or less?

Having just finished the newest book, Dexter is Delicious, I’ve started thinking on this again. What makes a book cross from mystery with speculative elements to full-on speculative fiction? After all, the only speculative element of the series is the Passenger. But, it’s a huge part of the series. Its existence drives the plots of the books, the development of all the characters and how they interact with each other, whether they know that they’re conversing with a “monster” or not.

It seems to me that books cross the line into supernatural noir when there are outwardly distinguishable paranormal agents involved—vampires, werewolves, fairies, whatever. I’d never call the Dexter series supernatural noir—it’s definitely labeled “mystery/thriller” in my head.

But, but... really, they kind of are supernatural, at least in part. I suspect it’s what makes me enjoy them so much, beyond the witty writing. The Dark Passenger is a sibilant whisper for our dashing Dexter, and so it is for the reader, as well. It adds a level of scary, surreal description to the books that the TV show willingly ignores, posits a universe very different from ours in a fundamental way—after all, if all predators have a Dark Passenger guiding them, where do they come from? If they are really alien, Other, what do they want, beyond carnage and satisfaction?

They’re interesting questions. And, if Lindsay chooses to turn the series in a direction to answer them more than solve murders and do detective work, the books might make the jump to a different section of the bookstore.

Genre is such a fun toy.

Brit Mandelo is a multi-fandom geek with a special love for comics and queer literature. She can be found on Twitter and Livejournal.