Author Justin Cronin returns to Portsmouth with ‘The Twelve,’ the sequel to his apocalyptic vampire epic ‘The Passage.’

As he prepared to write the second installment in his trilogy of post-apocalyptic vampire novels, author Justin Cronin confronted a problem he calls the “volume two trap.” The first book, “The Passage,” was a New York Times bestseller in 2010, earning Cronin legions of fans. Living up to their expectations while advancing the story and building a narrative bridge to the third book was a unique challenge.

“There’s a tendency for the middle book to feel really like the middle child. It’s just kind of getting from one to three, from the oldest to the youngest, and the middle one is just kind of that kid that’s hanging around,” Cronin told a roomful of avid fans at RiverRun Bookstore in Portsmouth on Oct. 18.

To work around this trap, Cronin decided not to follow a classic chronological timeline. Instead, he went back to the beginning, filling in gaps, inventing new plotlines, and expanding on characters or events that were only touched on in the first book. Careful readers of “The Twelve” will pick up on those loose threads, while also gaining a whole new perspective on the end of the world. 

“It is a continuation of the story, but I also wanted each of the novels to kind of set their own turf,” Cronin said. “I wanted each of the novels to have a sort of hard jerk in the front that changed the course of the story.”

Like its predecessor, much of “The Twelve” takes place in Year Zero, when a failed military experiment unleashes a pestilent virus that decimates the population, turning people into bloodthirsty monsters. But it also jumps ahead to the year 97 A.V. (After Virus), following the minority human survivors through an American wasteland as they attempt to hunt down the 12 original infected persons.

Though some readers were not keen on the first book’s 100-year gap, Cronin promised their patience would be rewarded.

“That hundred-year jump in the first book, some people loved it and some people wanted to smash my head against a windowsill for it,” he said. “But for those of you who survived and are here this evening, you now know how to read me. If you spend some time in Year Zero, it matters for the later story.”

Cronin last visited RiverRun in June of 2010, following the release of “The Passage.” Noting that former RiverRun employee Michele Filgate was an early advocate of the book, he said he made a point of coming back.

During his latest appearance, he read from “The Twelve” before taking questions from the audience. The segment he read focused on a character named Bernard Kittridge, known to the dying world as “Last Stand in Denver” (who, for those paying close attention, was briefly mentioned in “The Passage”). Holed up in a high-rise apartment in the otherwise abandoned city, Kittridge passes his nights sniping vampires with a rifle and posting videos of his exploits online.

Cronin, a New England native now living in Texas, actually practiced firing a rifle in order to write the part—a skill he learned from his dentist.

“For ‘The Passage’ I learned an awful lot about hand guns, and let me tell you, going to the shooting range on your lunch hour is a really good time,” he said. “To write this book, I had to learn to be a sniper. I had to learn to shoot a high-powered rifle.”

That sort of hands-on experience is typical of Cronin’s research. For “The Passage,” he traveled the same route that a group of characters took as they trekked across the West, visiting every town and location mentioned in the book.

“All the details of their journey from Southern California to Colorado correspond to an actual geography. Everything is real,” he said.

That same attention to detail is evident in “The Twelve,” which maintains an agreeably fast pace, balancing meticulous character development with doses of bloody vampire action that erupt like an arterial spray. 

Cronin gave his local fans some exciting pieces of gossip to chew on. While plans for a film version of “The Passage” have been in development for the last two years (Ridley Scott’s production company bought the rights in 2010), Cronin said he will promote the idea of making the entire trilogy into a three-season HBO series. The suggestion drew an excited murmur in Portsmouth.

Also, although the third book in the trilogy will offer a satisfying conclusion to the story, he is scheming a fourth installment.

“Believe it or not, despite the length and capaciousness of these books, you have no idea how many other stories of these characters and this world have been left on the cutting room floor,” he said. “There’s all kinds of other stories I want to tell.”