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, she learns that 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.

Unfortunately, she soon finds she is caught between two warring sides: on one, her mortal enemies, the alien Trackers, and on the other, the American government.