The story revolves around Kim Sun-yi (Park Bo-young), a teenage girl sent to the countryside for her health, where she discovers a feral young man (Song Joong-ki) hiding in the barn. He has been living in the wild, possessing animalistic behaviors and an inability to speak. Sun-yi names him Chul-soo and attempts to "civilize" him, teaching him how to eat, dress, and behave like a human. As they bond, a gentle romance blossoms, but their happiness is threatened when the true nature of Chul-soo’s existence—a genetic mutation that turns him into a werewolf—is exposed to the village.
