BROWNSVILLE, Tex. — It was the first time Domingo Martinez had returned here in nearly 10 years, and it seemed as if nothing and everything had changed. His street, once rutted caliche, was now potholed pavement. Favorite stores had shuttered, but new mom-and-pops still sold tamales and tacos, and the 18-foot border fence between the United States and Mexico slashed rust brown through farmland panoramas.

Mostly, Mr. Martinez marveled at how the decade had worn on his grandmother Virginia Campos Rubio, softening that gun-slinging lioness into a slow-moving 85-year-old with a gentle smile. Ms. Rubio is one of the central characters in Mr. Martinez’s book, “The Boy Kings of Texas: A Memoir,” which is a finalist for the 2012 National Book Award in nonfiction. In the book Mr. Martinez describes how an abusive, starvation-plagued childhood filled Ms. Rubio with rage, making her both loved and feared in the barrio where he grew up. She still keeps a pistol on her bed, alongside a copy of the Bible, a doll and a bag of cheese puffs.

At 40, Mr. Martinez has spent most of his adult life both running away from that Brownsville neighborhood and revisiting it through his prose.

He’s decidedly the underdog in the National Book Award contest. He’s the only finalist in the nonfiction category who has not won a Pulitzer Prize, the only first-time author, and the only nominee to have never been on the staff of The New York Times, The Washington Post or Newsday. Until a few months ago, Mr. Martinez was selling business cards at a print shop near Seattle, where he lives.