This taut and tense thriller from South Korea stars Kim Kang-woo as Cheon-soo - a swimming instructor who reaches end of his tether when a gambling loss leaves him with years of crippling debt. An "out" suddenly arrives in the form of an offer from moneylender Kang (Jo Jae-hyeon) - one that promises to rid Cheon of his woes. Yet the solution also courts enormous risk: Kang proposes that he quickly work off his debt as a "marine boy" - a courier required to smuggle drugs by swimming great distances across the ocean. Realizing that his life already teeters on the edge of a precipice given the pay-or-die demands of the men he owes, Cheon opts to risk everything in the said capacity. The plot thickens, however, given the involvement of Yoo-ri. The latter is a young woman raised by Kang, her father's best friend, after her father mysteriously died. Yoo-ri strongly believes that Kang rubbed out her dad, and thus quietly plots vengeance against Kang. When Yoo-ri meets Cheon, romance blossoms between the two, and the lovers plan to abscond with the drug money and escape from the shadow of Kang's control.
by Nathan Southern synopsis