Boneshaker

Thus was Dr. Blue's Incredible Bone-Shaking Drill Engine born. But on its first test run the Boneshaker went terribly awry, destroying several blocks of downtown Seattle and unearthing a subterranean vein of blight gas that turned anyone who breathed it into the living dead.

Now it is 16 years later, and a wall has been built to enclose the devastated and toxic city. Just beyond it lives Blue's widow, Briar Wilkes. Life is hard with a ruined reputation and a teenaged boy to support, but she and Ezekiel are managing. Until Ezekiel undertakes a secret crusade to rewrite history. His quest will take him under the wall and into a city teeming with ravenous undead, air pirates, criminal overlords, and heavily armed refugees. And only Briar can bring him out alive.

-Goodreads