When Veronica Roth graduated from Northwestern in 2010, at age 21, she had just sold her first book, which she'd written over a period of 40 days earlier that year. The whirlwind process, which Roth recorded on her blog—composing the first draft, finding an agent, revising, expanding, revising again, submitting it to publishers, and getting a book deal—had taken less than five months. In an entry from April, two weeks after HarperCollins picked up not just one book from Roth but a full trilogy, and two months before her college graduation, she wrote, "What if everything goes well?"

It did. Divergent, the first in a dystopian young adult series set in Chicago several hundred years in the future, debuted at number six on the New York Times best seller list in 2011. Its sequel, Insurgent, debuted at number one a year later. The two books have sold more than five million copies worldwide; they're still on the Times YA best seller list, waiting patiently to be joined by the final installment, Allegiant, which was released this week. A movie of the first book, starring Shailene Woodley, Theo James, and Kate Winslet, was filmed in Chicago over the summer.

Now, at age 25, one of the best-selling authors in the world, Roth lives in Edgewater with her husband. We had lunch last month to discuss the new book, our worst fears, and how she found time to write a novel while finishing college. Roth, a creative writing major, worked on Divergent when she wasn't doing homework, and started attending writers' conferences and querying literary agents her junior year—always without mentioning her age. "I'm kind of stunned by the unintentional arrogance of writing something and thinking, 'OK, I'll go try to get it published,'" she says. "It just didn't occur to me that maybe it wasn't good enough."

I asked her where this accidental moxie came from—what would lead a college senior to write a novel while her peers applied for internships. "It's really the only thing I've ever loved to do," she said. "The thought of being in a cubicle or doing a normal job made me want to cry, because it would take me away from this thing I wanted to do so much, so I think I tried because I was kind of desperate to do it."

It didn't hurt that Roth was in the right genre at the right time. When she was writing Divergent, the Twilight saga had just ended and the third book of the Hunger Games trilogy was seven months away (though both of those movie-franchise money trains were chugging along). Publishers were unlikely to ignore a young author with a YA dystopian trilogy in her pocket.

Not that she was jumping on a bandwagon. Roth, who grew up in Barrington, says she's been writing fiction since sixth grade: "Kind of similar to what I'm writing now. Speculative fiction of all kinds, usually featuring younger characters. So, the same," she laughs. A voracious young reader as a kid, she was a fan of YA staple Lois Lowry and, perhaps less predictably, of classic sci-fi like Ender's Game and Dune. Her own fiction reflects these dual interests—the trilogy boasts as much political scheming and hand-to-hand combat as soul-searching and steamy make-outs. Her agent pitched it to publishers as "The Hunger Games meets The Matrix."

Ryan Lowry

Divergent is the story of 16-year-old Beatrice Prior, who goes by Tris, deciding what kind of person she wants to be—a common enough process made slightly more complicated by Tris's environment. All members of her society, when they turn 16, choose a faction. Those factions represent different values that the society has chosen to cultivate, and therefore that their members devote their lives to. And there are only five options.

The members of Abnegation value selflessness; the members of Candor, honesty; the members of Amity, peace; the members of Erudite, knowledge; and the members of Dauntless, bravery. As one of the society's leaders explains, "Decades ago our ancestors realized that it is not political ideology, religious belief, race, or nationalism that is to blame for a warring world. Rather, they determined that it was the fault of human personality—of humankind's inclination toward evil, in whatever form that is. They divided into factions that sought to eradicate those qualities they believed responsible for the world's disarray."

All 16-year-olds go through a simulated aptitude test that determines which faction they're best suited for by recording their reactions to difficult situations, such as whether to throw yourself in front of a vicious dog to prevent it from attacking someone else. (The simulation is triggered by a serum that overrides the brain, and is the first of one of the trilogy's hallmarks—a trip into a character's subconscious.)

You can choose to become a member of any faction, regardless of your aptitude, but the majority of people stay in the faction that raised them. Tris was brought up in Abnegation. All her clothes are gray; she looks in the mirror only once every three months. Members of Abnegation walk softly, put others' needs before their own, and eschew personal possessions. Tris chafes at this lifestyle, and worries her aptitude results will prove that she can't hack the simple life.

But her test is inconclusive. She shows aptitude not for a single faction but for three—indicating that she is, as she's told ominously, "Divergent." It's not a good thing. As someone later explains to her, "Our minds move in a dozen different directions. We can't be confined to one way of thinking, and that terrifies our leaders. It means we can't be controlled."

Roth says that she probably would have chosen Abnegation herself, but then "not have been able to hack it and gone rogue—factionless." (After Divergent, factionless is the worst thing you can be.) "I have this long-standing fascination with personality tests. I was obsessed with defining myself or fitting myself into a category, and as I grew older I realized how harmful that is. It doesn't allow you to grow. Maybe the book is grappling with that."

Tensions are brewing among the factions, who, in their pursuit of their individual values, have lost the ability to understand each other. The virtues, as an end to themselves, have warped and dulled. The Dauntless can be needlessly cruel, the Erudites are snooty and manipulative, and the Abnegation are boring everybody else to death. Among the great dystopias of literature, this is a rare one whose fatal flaw is its good intentions.

The contentiousness makes it controversial to transfer from one to another, as Tris does, to Dauntless. To pass initiation and secure membership, Tris has to learn a lot of kick-ass stuff, like throwing knives, shooting guns, and jumping onto moving trains. She also has to endure a lot of torment, like a series of simulations that make you confront one of your worst fears and don't end until you either defeat it or calm down. The final exam is a complete run-through of all your worst fears, aptly and invitingly called a fear landscape.

Tris doesn't get her fearlessness from Roth, who admits that, as a teenager, "I wanted to be like Tris. I think that was the kind of attitude I projected. She's kind of tough, not particularly nice, doesn't let people walk on her. I think I really wanted to be like that but really I had this incredibly soft underbelly." When I ask what would be in her fear landscape, she replies: "Like, everything."

Tris is described as short, blond, and "birdlike," while Roth is a six-foot-tall redhead who is thoughtful, gracious, and unexpectedly funny for someone who writes such a drum-beating series. Having read two books about Tris and had lunch with her creator, I can confirm that Roth is the better hang.

When she's not being physically or psychologically tortured, Tris falls in love with her new faction, and for this Roth makes good use of the city. The factions are spread thinly over the ruins of Chicago, inhabiting a small number of buildings while the rest stand vacant. The Dauntless headquarters are underground, somewhere on the south side, but Erudite is ensconced in Millennium Park, and its members hang out at the Bean. Candor's headquarters are in Merchandise Mart, where, Tris thinks, "it must be easy to get lost . . . since everything looks the same." (The idea that generations from now people will still be getting lost in Merchandise Mart may give the Chicago reader a pleasing sense of constancy).

For fun, members of Dauntless zipline off the Hancock building. Elsewhere they can be found playing high-stakes games of capture the flag in the middle of the night on Navy Pier. It's during such a game that Tris climbs to the top of the Ferris wheel to scout the other team's flag, accompanied by her hot, brooding initiation instructor, Four.

"Theo and Shailene actually climbed that Ferris wheel!" Roth reports. She visited the set a few times during filming. "It was extremely weird to see famous actors act out scenes you've written and then get on the Red Line and go home like it was any other day." Although she's had long conversations with Neil Burger, the movie's director, she otherwise limited her contribution to the production to enthusiasm. She's happily reported on her blog that the costumes look amazing, James and Woodley have great chemistry, and the pivotal Ferris wheel scene went off well. Roth includes heights in that encyclopedic fear landscape of hers, which gave her visit to the set on the day that particular scene was filmed an accidentally sadistic bent: "I just watched from the ground and thought, 'I can't believe you just did that!'"

Ryan Lowry

Ryan Lowry

The Ferris wheel scene is the beginning of Tris and Four's romance, it's a turning point for her role within Dauntless, and it's when she begins to learn that using her divergent, non-Dauntless qualities—such as strategic thinking—can be a good thing. Its multipurpose nature is typical of the trilogy, where action in the story is often mirrored by intense introspection. (Four, for instance, leads Tris through his fear landscape before he even kisses her for the first time.) Leaving Abnegation for Dauntless was an enormous show of independence on Tris's part, and the rest of the book has her wrestling with why she made that choice, whether it was the right one, and where exactly she belongs, if anywhere.

I asked Roth about the trilogy's exploration of free will in a society designed to stifle it, and what in our world prompted that particular dystopian vision. "I think it's a little more personal than that," she says, mentioning the anxiety disorder that she's written about in the past. "I feel very confined by my fear a lot of the time, like Tris feels in Abnegation, and then to have her choose something so bold and freeing and scary was almost my way of testing that out. It was kind of like a safe place to explore this need to escape my own brain."

But even as Tris struggles against the confining faction system, it starts to fall apart. At the end of Divergent, one faction attacks another, and Insurgent follows the ensuing war. Factions fracture and realign, and new alliances are formed along political rather than personal lines. Tris and Four make allies and enemies in each faction as they search for the truth about the war they're fighting and what it might have to do with the very origin of their society.

In the first two books, "[Tris's] world expanded from Abnegation to Dauntless, then to interacting with other factions. In the third book it will expand even further," Roth says. The end of Insurgent set up a conflict that escalates beyond the factions. As one factionless character puts it, they were waiting "for the world to fall apart. And now it has." I ask about the potential body count. Roth says she "might have been more cold-blooded" in the new book, and then coyly takes a sip of water.

Death and destruction aside, many of Roth's fans will open the book on publication day to see if Tris and Four hit the sack, a development that's been much clamored for and vaguely promised. Once Allegiant is in the hands of her readers and all questions of love and war have been answered, Roth says, she's looking forward to some time away from the trilogy, which she's worked on constantly since 2010—and to writing for fun again. She's maintained that she'll keep writing for a teen audience, but she doesn't know what or when that will be.

A lot of 25-year-olds don't know what to do with themselves, but it's not usually because they've already had a lifetime's worth of success. Roth isn't afraid of the downtime. "I've never had any hobbies because I just wanted to [write] all the time. And now it's a problem because it's what I do all the time for work and I don't have any hobbies. Maybe I'll get hobbies."