The day the sun disappeared forever behind the clouds, legendary monsters that had been seen only at night began to crawl perpetually, and the human fear of being hunted ubiquitous. For almost 30 years, Lame and her village have been cut off from the rest of the world. The monsters, who track the villagers by sound and especially by voice, have forced them to communicate by sign language. But their safety is endangered when a young woman called Moon, who wears strings of little bells, arrives in the village. She tells them that there is a way of fighting the monsters: by becoming monsters themselves.