Former national swimmer Cheon-soo dreams of travelling to Palau, and to fund his trip he works as a swimming instructor by day while gambling at night. However, after losing a game of poker he finds himself heavily in debt and in trouble with the loan sharks. Kang, the head of a local drugs syndicate, offers to pay off Cheon-soo's debts; in return, Cheon-soo must work as a "marine boy", a mule who smuggles drugs across the open waters.
Knowing the danger he faces, Cheon-soo tries to make a run for it, but he is arrested at the airport by police detective Kim Gae-ko. Kim is intent on capturing Kang, and faced with no other choice, Cheon-soo agrees to work as a spy on his behalf. His situation becomes further complicated when he falls for Yu-ri, a jazz singer under Kang's charge and the daughter of Kang's best friend. But Yu-ri suspects Kang of killing her father, and she and Cheon-soo plot to take the drug money for themselves.
Who  offers to pay off Cheon-soo's debts?
Kang, the head of a local drugs syndicate, offers to pay off Cheon-soo's debts