The Fortress - T. A. Styles - Bog

We are the fortress, and the fortress is us.

Sim was a teacher in his old life. Now he's the savior of orphans.
He isn't their father. God knows he has already failed in that role. But he is their guide. And the kids? They are his penance. His redemption.
For three years Sim has prepared his orphans for the hard realities of life after the plague that wiped out most of the global population. Theirs is a life without laws or creature comforts. He has trained them to forage and grow their own food, to be vigilant, and to protect themselves and each other by any means necessary. In building a fortress of brick and mortar, they've become a fortress of flesh and blood.
These allegiances and ideals are put to the test when a man named Zagan, who believes himself to be on a mission for the devil to bring about the destruction of civilization's remains, gathers hundreds of marauders and confronts Sim and his orphans in a merciless siege.
Will the fortress hold... Or will it collapse under the pressure of evil?