The Variant Saga Boxed Set

After an toxic gas named Variant, the world is destroyed and the remaining people are living underground. Set in the futur after the catastrophy, they rely on a group of «Mothers» who are tested at a Young age to repopulate the world. Maya is one of their top «Mothers» and one day she agrees to carry a child without knowing anything about the father. Her son Terry is not like the others, he's altered. On 7th birthday, he's happy because he's going to his first day of school. What he doesn't know is that the moment he sets foot in the school he's staying for the next 10 years to be trained as a soldier. The most bizarre is that a lot of kids are also celebrating the same birthday as him and are selected to become soldiers too.
As the years go by , we see them grow up, trained and educated all part of the of the plan to try to go back to the surface.

It was a really great story, well written and the mystery and suspense made you want to read more of the book. The ending does not disappoint.