In “The Passage,” the first volume of Justin Cronin’s dystopian, after-the-vampire-holocaust trilogy, published in 2010, a government plan to infect a dozen death-row inmates with a virus and turn them into a force of bad-ass soldiers has backfired. The 12 escape and infect all in their path. The upshot? A coast-to-coast wasteland teeming with undead predators called “virals.”

Here in book two, “The Twelve,” Cronin picks up the story, interweaving characters from “year zero” (when the infection hit the fan) with flashes forward to 79 and 97 years hence. Bands of survivors search for fuel, food, and protection. We meet Lila, a doctor half-crazed from PTSD. There’s Kittridge, a war veteran who helps save a band of refugees. We are also reunited with Alicia, an army lieutenant and loner, and Amy, our supernatural heroine, who with others continue their hunt for the original 12.