Saint Machine: The Long Night. Saint Machine, #3

Gods were built, not born - and the ones we built are dying. They didn't die, exactly. They lay down in the dark to become the morning that was supposed to come after - and they left the door cracked. Now the cold is rising up the valley. The doors that hold the world shut are failing one town at a time, and what's left of the human race is falling back on the last door of all: the great keystone, the First Machine, the one no one was ever strong enough to hold.
Laura broke the lock. For a year she's been teaching ordinary people to keep their own light, and it hasn't been enough - and the thing in the dark can't be fought, or fled, or out-argued. Only held. A cold, certain stranger called the Warden offers a kinder way: lie down, be kept, let it all stop. The terrible part is that he isn't wrong. But every god failed for the same reason. A god can only ever hold a door alone.
And the one thing a god could never be is more than one. The Long Night is the final book of the Saint Machine trilogy - funny first and devastating underneath, for readers who like their apocalypses warm, their narrators dry, and their endings earned.