Skyhunter by Marie Lu

The Karensa Federation has conquered a dozen countries, leaving Mara as one of the last free nations in the world. Refugees flee to its borders to escape a fate worse than death—transformation into mutant war beasts known as Ghosts, creatures the Federation then sends to attack Mara.

The legendary Strikers, Mara’s elite fighting force, are trained to stop them. But as the number of Ghosts grows and Karensa closes in, defeat seems inevitable.

Still, one Striker refuses to give up hope… Read more.