Seventeen years old is much to young to take on an entire alien empire.
When the small communities of Corros, a remote human colony world, come under attack from the Tolleani, an alien species with whom humanity is at war, Echo, a young woman, finds herself the sole survivor.
For three years she survives alone, wondering why nobody has come to rescue her. Then, the aliens return to set up a research base at the community which had once been her home. For another year, she hides alone in the nearby mountains, until the first human ship arrives, to be promptly captured by the aliens.
When Ben, a member of the captured crew, escapes, he stumbles upon Echo's hideaway. She needs his help to escape, but soon learns that he has an agenda of his own, and needs her help to achieve it.