I wrote my first mystery novel by accident. One sunny morning in the summer of 2003, I started a short story about a murder in Victorian London, and when I came up for air several weeks later I had 200 pages and absolutely no idea who the murderer was. I chose one over lunch, and though I’d like to warn aspiring authors that this is the least intelligent way to do things, I eventually made the crime stick to him.

This bit of summer carelessness has had far-reaching consequences: I’ve now written seven books in the same series—more than 2,000 pages in print about a galaxy of characters I’ve come to know and love. Ten years have passed in real life, 11 in the series (which covers 1865–1876). My protagonist has acquired a wife (same here) and a child (not quite yet). The books have sold well, received generous reviews, and, best of all, found an ardent group of readers. When I write one of them now, I generally know the murderer’s identity before I’ve set down a single word.

And it still feels like an accident.

My chief passion as a reader was always literary fiction. There are genre writers I revere—Elizabeth George, Arthur Conan Doyle, Dick Francis—but I haven’t cared about them in the way I have about David Lodge and Alice Munro, George Orwell and Leo Tolstoy, the literary novelists (though I dislike that term) whom I’ve carefully gathered into a list in my mind over the years, the ones whose humanity taught me the most about life.

It’s true that the publishing industry takes the division between literary fiction and genre fiction more seriously than readers do. For instance, another member of my little mental coterie is Patrick O’Brian, whose nautical novels have the definite feel of genre fiction at first glance. Then there are the authors who defy classification: is Richard Price, whose books have such impeccable police-procedural plotting, an exalted crime writer or a gritty literary novelist? What about Jonathan Lethem and Paul Auster, literary writers who (like Dickens) nearly always seem to draw on the language of the mystery?

Still, I know where my own books stand. After all, they’re mysteries set in London in the Victorian era—a period that elicits very definite expectations from its readers. And then, I’ve produced so much. A book a year! There’s something graceful about long silences. Jeffrey Eugenides publishes every few centuries or so, and that feels like the tempo of real thought, unmotivated by concerns of commerce or entertainment.

The whole question has become more than academic to me, recently. After years of working on it (far longer than any mystery has taken me to write), I’m scheduled to publish, in January, my first nonmystery novel, The Last Enchantments, about a group of students at Oxford—sort of Brideshead Revisited meets Prep, we hope.

It’s an intimidating transition. Not many writers can shift out of their established identities (though the examples of Jess Walter and Kate Atkinson, who started out writing crime fiction, are inspiring). Still, I had imagined this moment for such a long time that the challenge didn’t faze me. Liberation! I was ready to ditch the comfortable, marginal world of genre and enter the great arena of art.

In fact it hasn’t been like that at all. As The Last Enchantments gets nearer to publication, instead of sailing gleefully away from those seven mystery novels, I keep turning to look back, fascinated. The fact is, they’ve given me a great deal of joy: writing them, editing them, seeing them in bookshops—the usual jumble of ego and passion that drives all writers. On a more practical level, they taught me an enormous amount, in a Gladwellian 10,000-hours sense. (If you want to learn to write novels, I can’t recommend a better apprenticeship than cranking out seven of them in 10 years.) I think the truth is that they were the books I was ready to write, when I wrote them. There’s nothing accidental in that.

Now January is approaching. I used to imagine that once I started writing literary novels, I would write them exclusively, and give up mysteries; isn’t there something faintly irreligious—even dilettantish—in writing across two styles?

All I know is where my heart lies. Last week, going over the proofs of my big literary novel, over whose words I agonized for so long, I had a wistful longing for the less difficult pleasures of 1876. Sitting in the park where I sometimes work, I opened, almost involuntarily, a new document on my computer, and typed, with a feeling of happiness and homecoming, two familiar words: “Chapter One...”