Afflicted with amnesia, the woman—who christens herself Nilla after a box of vanilla wafers that constitutes one of her first meals as a zombie—is obsessed with two things: her past and her future. She is driven to discover her lost identity, as if this information will restore her to what she was. At the same time, self-preservation impels her to flee the increasingly violent and desperate actions of civilian and military forces fighting their own battle to survive—a battle those of us who have already read Monster Island know is a doomed one.

Just as Gary, the doctor turned zombie who became one of the chief villains of that book, gains unexpected psychic abilities in his transformation from living to undead, Nilla finds herself suddenly able to, Shadow-like, "cloud men's minds," effectively rendering herself invisible for short periods of time. In addition, she becomes aware of a golden energy that suffuses all living things, energy that reaches its height in human beings; zombies like herself are filled with a dark, smoky energy. It is not living flesh and blood that zombies gorge on, but this golden energy, which temporarily banishes their own unbearable darkness of unbeing.

Again like Gary, Nilla is contacted by Mael Mag Och, whose mummified corpse resides in New York's Metropolitan Museum of Art. Mael uses coercive telepathic powers to direct Nilla's steps ever eastward: There she will join him and Gary in wiping the stain of humanity off the planet. But Nilla is also drawn toward a mysterious mountaintop compound in Nevada that may be the source of the zombie plague—a plague that she, and she alone, may have the ability to cure.

Meanwhile, Capt. Bannerman Clarke of the Colorado Army National Guard is after Nilla for reasons of his own—the ramrod-stiff, by-the-book officer suspects that she is the key to the nightmare that is swiftly engulfing the entire country. But his heroic efforts may only be playing into Mael's hands.

Character-driven horror with a sci-fi gloss

Like its predecessor, Monster Nation was originally posted in online installments, and the novel retains all the addictive and propulsive narrative energy of serial publication at its best. The blazingly fast spread of the plague, accompanied by dramatic breakdowns in authority and sanity, makes for riveting reading. Wellington ratchets up the suspense even further, and provides a sense of verisimilitude as well, by interspersing his text with material purportedly drawn from blogs, e-mails, graffiti and so on, a diary of the doomed.

As in Monster Island, it is strong characterization that really propels the narrative. Nilla is a superb creation. A zombie with a conscience, she becomes the most sympathetic of the cast, and her struggle to retain her humanity despite her condition is a moving one. Clarke, while a tight-ass, proves to be a genuine hero, noble and brave almost despite himself. And then there's Dick. A field agent for the NIH, Dick is an early casualty of the plague who reanimates to find himself bereft of arms. This sick joke of a zombie, who makes up in appetite and determination what he lacks in appendages and brain power, is recruited by Mael to be Nilla's accomplice, whether she likes it or not.

But for all its virtues, Monster Nation doesn't rise to the level of Monster Island. Partially this is because anyone who has read the latter already knows whether Nilla's quest ends in failure or success. It's hard to generate suspense when the outcome is never in doubt, and though Wellington does an exemplary job, the problem keeps cropping up throughout the novel, robbing his plot, and especially its climax, of unpredictability, the invigorating sense that all bets are off and anything might happen. That's always a problem in the middle books of trilogies, but by making Monster Nation a prequel, Wellington exacerbates it.

Wellington's take on zombies remains refreshing and witty, but it's no longer new, and what new material he does add, mainly a pseudoscientific explanation of the plague that invokes rather than incorporates the theories of Rupert Sheldrake, doesn't feel sufficiently thought out. It's the literary equivalent of duct tape: not pretty or elegant, but it holds things together well enough as long as you're reading fast ... and you will be.