The Dark, Paperback/James Herbert

A blackness leaves its lair, and begins slowly to spread It came like a malignant shadow with seductive promises of power. Somewhere in the night, a small girl smiled as her mother burned, asylum inmates slaughtered their attendants, and in slimy tunnels once-human creatures gathered. Madness raged as the lights began to fade, and humanity was attacked by an ancient, unstoppable evil.