The Proving by Ken Brosky
It's been 100 years since the Specters invaded Earth. Like ghosts they haunt the planet, devouring any human being foolish enough to venture outside of the last remaining protected cities. For some humans, venturing out isn't a choice--it's an opportunity to prove yourself to your clan. But when a coterie of New Adults undertaking a mission deep in Specter territory discover a terrible secret, they quickly find that everything they've learned may be wrong ... and Earth is in grave danger.