The Gathering Dark. Graham's Resolution, #12

The sirens called the surviving Watchers home. They were not the only ones listening. For fifteen years, Hanford survived by remaining silent-its reactors guarded, its secrets buried, and its people hidden beneath the Burning Ground. Now the silence is over. Watcher stations have gone dark. Records are missing. Refugees are being driven toward the basin. And beyond the eastern ridges, a disciplined army is gathering under the command of a man who knows Hanford's procedures, its defenses, and the doctrine that kept it alive.
He was once one of them. As winter begins to break, Graham must prepare his people for an enemy unlike any they have faced before-one who understands that Hanford's greatest weakness is not its walls, but the choices made by the men who built them. To survive, Graham and the others must decide what they are truly protecting, what the past still demands of them, and how much of their humanity they are willing to sacrifice when the gathering dark finally reaches their door.
The Gathering Dark is Book 12 in the Graham's Resolution series, a gripping post-apocalyptic survival thriller about family, loyalty, sacrifice, and the terrible cost of standing watch.