Kim Seong-geun is deep in debt and his life seems completely hopeless. He jumps off a bridge into the Han River and washes up on the shore of Bamseom,
which lies directly below the bridge. After searching the island he finds it is filled mostly with vegetation and surrounded by the city, but too far to shout and he can't swim. He finds a duck-shaped paddle boat and begins to like living on the island—free of his debt and worries of city life—though it is not easy.As he learns to survive on the island, his cry for help scrawled in the sand is seen by Kim Jung-yeon a hikikomori who spots him while engaging in her nightly habit of photographing the moon. They soon begin exchanging messages, with Jung-yeon venturing out of her house at night to throw bottled messages
onto the island, and Seong-geun writing his replies in the sand. Seong-geun also manages to cultivate crops to prepare noodles for an instant noodles packet of jajangmyeon.
A torrential storm arrives, destroying Seong-geun's farm and sweeping away the possessions he has collected. He is found by a group of workers sent to clean up litter on the island and forced off. Seong-geun boards a bus in the city to jump off the 63 building.
Jung-yeon, who, after overcoming her anxiety and desperately running across the bridge to find him, manages to catch up to his bus after the civil defense drill stalls it. She boards and introduces herself to him.