The year is 1907. An alternate 19th century powered by steam engines filled the sky with smog and erased humanity's memory of blue skies. Nowhere is darker than New York — five years ago the entire city was destroyed in the event called the Great Disappearance, sealed off from the world and left in silence. A woman named Elysia enters the ruins heading toward old Manhattan, seeking the epicenter. She does not know about the Underground: a vast subterranean realm lit by violet light, where the skyscrapers that crumbled above still stand in warped form. The people who vanished five years ago are still alive down there — surviving in terror, hunted by seven creatures called the Messengers. A girl named Lily arrives in the Underground with no memory, carrying a certainty she cannot explain: she has to reach the tower visible in the distance. She sets off anyway.