The Walled City, Paperback/Ryan Graudin

730. That's how many days I've been trapped. 18. That's how many days I have left to find a way out. Jin, Mei Yee, and Dai all live in the Walled City, a lawless labyrinth run by crime lords and overrun by street gangs. Teens there traffic drugs or work in brothels--or, like Jin, hide under the radar. But when Dai offers Jin a chance to find her lost sister, Mei Yee, she begins a breathtaking race against the clock to escape the Walled City itself.