Boneshaker, by Cherie Priest.
Seattle, 1879. Sixteen years earlier, Leviticus Blue created a drilling machine — Dr. Blue’s Incredible Bone Shaking Drill Engine — that destroyed the business district and released Blight gas that kills you undead. Seattle had been abandoned to the Blight gas and the “rotters” behind two-hundred-foot walls. Blue’s widow and her teenage son, Zeke, now live in the poor district just outside the walls where she makes a living in the water processing plant. Both are shunned and still harrassed for what Leviticus did to Seattle.
One day, Zeke sneaks into the city, determined to find out what really happened. His mother goes after him to bring him back.
Even though the book runs 400 pages, it was a fast read. Fast-paced adventure involving airships, mad scientists, flesh-eating undead, steampunk machines, ruined tunnels, poison gas. Fun stuff. I’m not really sure about the big bit at the end, though. It seemed to just… happen.
Book 1 in the Clockwork Century Universe. Nominated for the 2010 Hugo Award for Best Novel.