Teenager Aster barely escapes with her life when her adoptive father is killed in a shooting. Suddenly finding herself under the protection of a special US military unit, blood tests indicate that she's not even human.

Unsure who or what she might be - or if any of this is true - Aster's first instinct is to flee.

Soon she is caught between two warring sides: on one, her mortal enemies, the alien Trackers. And on the other, the American government.

Now Aster can be certain of just two things:

Her blood is more vital than she ever knew. And the fate of the world rests upon her survival . . .