Black City, book 3: WingsElizabeth Richards2014

Natalie finds herself separated from Ash and unexpectedly reunited with her parents, including the father she thought was dead. But she can only think of Ash. She hasn't heard a word of him since she and Elijah were brought to the underground headquarters of the Sentry Rebellion. But she vows to find him.

Ash, meanwhile is back in Black City; it's the perfect place to hide from the Sentry government. But not for long. He won't give up on Natalie or bringing an end to the terrible reign of Purian Rose.