In “Sector 7”, an underwater oil field located south of Jeju Island, Hae-jun is working as a marine equipment manager on an old oil prospecting ship called Eclipse with Hae-jun’s boyfriend and marine biologist Dong-su, fun-loving Sang-gu and a clueless new recruit, Hyun-wu. After 3 weeks of preparation, Hae-jun takes Hyun-wu underwater, but the new recruit sinks not an accident and points at one of the crew as a saboteur. Shortly crew members begin to turn up dead, one by one, their bodies viciously mutilated. What the few survivors soon discover is a transparent underwater creature that they encountered once before. The viral monster infiltrated the ship through the drilling pipe and has been feeding on the crew to survive. Hae-jun and her colleagues’ frantic fight for their lives begins