Paula Hawkins has made a heck of a debut. After Riverhead released her first book, The Girl on the Train, on January 13, it quickly topped a slew of bestseller lists—hitting #1 on PW's hardcover fiction list, and #4 on the overall bestseller list. In its short time on sale, the thriller has already sold more than 87,000 hardcover copies, according to Nielsen BookScan, which tracks roughly 80% of print sales. Riverhead reports that it now has more than 500,000 copies in print. The debate rages on as to whether or not the book will follow the publishing path of Gillian Flynn's Gone Girl (DreamWorks has already nabbed film rights to the title), but it is poised to be one of the first, and potentially the biggest, blockbuster book of 2015. We chatted with Riverhead editor-in-chief Sarah McGrath, who acquired the book, about its meteoric rise.

What do you think it is about this book, in particular, that is sending it up the bestseller lists?

The word of mouth has been contagious from the beginning. It has an enticing hook, one that appeals to the voyeur in all of us. And it’s a domestic, psychological thriller that reaches across category lines. It becomes a gripping whodunit, but the story is also propelled by themes of identity and envy and memory, marriage and motherhood and loss and responsibility. There’s a whole lot more going on here than just the solving of a crime.

What was the submission process like? What were your first-read reactions?

I wasn’t specifically looking for a thriller of any sort, but this came across my desk from the agent and something about it spoke to me immediately. I mean, haven’t we all done that thing of looking curiously into other people’s yards and windows as we travel by, speculating about the lives on the other side? I now know, having discussed this book with so many people, that I’m not alone in this nosiness. We are all voyeurs in this way. But Paula Hawkins found a way to take it even further, to consider how the world reflects back at us, in these nosey observations, our own complicated feelings about our own lives and selves. I loved that. And then she found a way to put more and more at stake. I read the manuscript in one greedy gulp, and then thought of it every single time I traveled to or from work. I looked at all the people on the train around me and thought, man, do I know a book you’re going to want to read.

Every season it seems like there’s a novel that draws Gone Girl comparisons. How do you think this book lines up and diverges with Gone Girl, and also, how does this Gone Girl-like novel differ from all the other Gone Girl-like novels?

I’ve been surprised by the frequency of that comparison. Though I loved Gone Girl, to me they are quite different books. I fell in love with The Girl on the Train because of its commuter conceit and the cleverness of the out-of-control, memory-blocked narrator. These were both things I hadn’t seen done before in this way, and they excited me. It’s true that like Gone Girl, The Girl on the Train uses an unreliable narrator (or, actually three, one of whom is unreliable even to herself), but to me the thing that keeps drawing this comparison is the fact that it is a psychological thriller with appeal that reaches wide across category and readership. Beyond that, they're very different books.

What was the in-house reaction to the novel being a hit so soon after publication? Were you surprised?

From the very beginning, enthusiasm for this book has been contagious. It was within hours of my introducing the book at our launch meeting last March that a parade of colleagues began showing up at my office door, begging to read it. A week later, a colleague was finishing it secretly under the table during a big meeting because she couldn’t stop. In the elevator I overheard numerous conversations trying to predict the ending. You know you have something special when your book becomes the water cooler conversation for the whole building. I’m surprised and impressed at the scale of the book’s success because it is so unusual for a new author to take off with such momentum, but I’m not surprised that the book is popular. Those signs have been there from the beginning. There is something about the idea of this book that makes people want to read it, and then, because the read delivers, to talk about it.