Army officer Kang (Jang Dong Gun) is stationed in Korea's eastern water regions. All seems to be quiet and peaceful here, but a notice warns that whoever comes to this place after seven o'clock at night will be regarded as a spy and executed on the spot. One night, Kang opens fire on a suspected spy, who turns out to be a local who sneaked in with his girlfriend. As the army believes that Kang's shooting of the man is in accordance with the rules, they allow him special leave to revitalize his spirits. However, Kang can't get over the terrible incident. After his leave period is over, he returns to his post, but is still unable to shake off his past experiences. His mental shape gets worse and worse and in the end he gets dismissed from duty and is sent back to Seoul. Yet Kang still believes that he is a member of the coast guard and heads out to visit his old post one more time.