After defying the ruthless Enclave, surviving the wasteland and over-throwing the tyranical leader of Sylum, Gaia Stone now faces her greatest challenge yet - to lead the people of Sylum back to the Enclave and persuade the Protectorat to grant them refuge.

With Leon finally by her side, Gaia is hopeful that she can settle her people and finally start the life with him that she always wanted.

But in Gaia's absence, the Enclave has become even more ruthless, picking girls from outside the wall to serve in an experimental baby factory. Babies with the right genes are now a priceless commodity with the potential to reshape life inside the wall and redefine humanity.

And when it becomes clear that her genes are exactly what the Enclave needs, Gaia is appalled by the lengths they will go to...