The Klints, a superior race in every way, long ago decided to abolish natural birthing; over the last millenniums, every child had been engineered, created, designed; but things went wrong, hence their need for human breeders.
Lena's life might have changed since their invasion, but she's not particularly affected by their presence on a daily basis, until the day they find out that she's a hundred percent compatible to the emperor of the entire galaxy.
Her job was simple. She was supposed to give birth to his heir and disappear.