From the Introduction:
Nobody remembers how or why. Maybe nobody ever knew. The oldest living survivors have childhood memories of it: cities burning, society in chaos then collapse, families set to panicked flight, the weird nights when the smoldering sky made midnight into a blood-colored half-day.
Now the world is not what it was. Look around you: evidently, certainly, not what it was. But also close your eyes, open your brain: something is wrong. At the limits of perception, something howling, everpresent, full of hate and terror. From this, the world's psychic maelstrom, we none of us have shelter.