The film tells the story of more than 400 Korean refugees who were forcibly conscripted to Japan's Gunkanjima during the Japanese colonial period, trying to escape to avoid being killed. In 1945, during the turbulent period when rumors were spreading as the war was about to end, Lee Kang-wook (Hwang Jung-min), the leader of the Peninsula Hotel Jazz Band in Gyeongseong, brought his only daughter Su-hee (Kim Soo-an) and the band, Choi Chil-sung (So Ji-sub), a boxer who dominated Jongno, and the youngest son (Lee Jung-hyun), who suffered under Japanese rule, and other Koreans, were deceived by the lie that they could make money and go to Japan, but they arrived at Gunkanjima, where Koreans were forcibly conscripted. In a mine 1,000 meters deep under the sea, they were forced to work under the danger of gas explosions. Lee Kang-wook tried every means to protect his daughter on Gunkanjima, and Choi Chil-sung and the youngest son also used their own methods to survive the painful days. After the war, OSS (US Strategic Intelligence Service) secretly instructed Park Wuying (Song Joong-ki), a key member of the Korean Independence Army, to rescue the presidential candidate Yoon Hak-cheol (Lee Kyung-young) who was hiding on Gunkanjima. In order to cover up all the crimes committed against the Koreans on Gunkanjima, the Japanese decided to blast the mine where the Koreans worked. In a critical situation, Park Wuying rescued Yoon Hak-cheol with difficulty and revealed his identity. The Koreans headed by Park Wuying, Lee Kang-wook, Choi Chil-sung, etc. were determined to escape from Gunkanjima. The director of the mine, who vaguely sensed the inside story, desperately chased them to cover up all the secrets of Gunkanjima.