Gu Chang leads to a tragic existence. The seventh-year college student constantly fails job interviews and lives off of an allowance from his divorced sister while taking money from his little nephew. To make matters worse, the almost 30-year-old virgin has never had a girlfriend, let alone experienced his first kiss. In Korean, Gu Chang is a homonym for the word meaning "a sore in the mouth".
But springtime finally seems to have arrived for Gu Chang, defrosting the stark winters of his barren love life, when he meets the sweet and innocent Ah Ni.
All seems to be well, and Gu Chang gets a taste of heaven as he kisses his pretty girlfriend for the first time - until Ah Ni bites his tongue and gives him a nice kick, introducing herself as Ha Ni. And so begins Gu Chang's painful relationship with his split-personality girlfriend, dealing with Ah Ni's adorably childish demeanors one moment, then defending his life from Ha Ni's high kicks.
Looking for a new start, a young taxi driver moves into Apt. 504 of an old tenement named Migum Apartments. He soon finds that the previous tenant died mysteriously, and everyone on the floor is connected to the man.
After befriending the neighbor living a few doors down, he falls into an affair that sends them both down a dark path. But there's something else odd about the atmosphere in the run-down building. Does a ghost haunt those living here, or does the evil exist in those left alive?
Nothing is more symbolic of the division of Korea into two countries as the 'Bridge of No Return' in Panmunjom, the demilitarized zone on the border between the two states. One day, a border guard is killed by a rifle bullet; the suspected marksman is a South Korean soldier, who is found wounded in the middle of no-man's-land. This incident will have grave repercussions. Both North and South Korea regard the incident as an act of deliberate provocation. The North accuses the South of having committed a 'terrorist attack', whilst South Korea suspects the North of having attempted an 'abduction'. Both sides appeal to the authorities of the neutral states (NNSC) for help and ask them to investigate the affair.
A female Swiss army captain of Korean descent is then sent to Panmunjom to investigate the death of the North Korean border guard, apparently shot in the line of duty by a South Korean guard. At first, neither army officers from the South nor communist officials from the North will cooperate - until it is obvious to all that the truth must come out to defuse a potentially explosive international incident.