Enclave (Razorland Trilogy #1)

New York City has been decimated by war and plague, and most of civilization has migrated to underground enclaves, where life expectancy is no more than the early 20s.

When Deuce turns 15, she takes on her role as a Huntress, and is paired with Fade, a teenage Hunter who lived Topside as a young boy. When she and Fade discover that the neighboring enclave has been decimated by the tunnel monsters  Freaks who seem to be growing more organized, the elders refuse to listen to warnings.

And when Deuce and Fade are exiled from the enclave, the girl born in darkness must survive in daylight, in the ruins of a city whose population has dwindled to a few dangerous gangs. As the two are guided by Fade's long-ago memories, they face dangers, and feelings, unlike any they've ever known.