In the southernmost waters of Jeju Island, the oil exploration ship "Eclipse" went deep into the oil development area of the seventh mining area 2,500 meters below the seabed to conduct oil exploration. The crew members are ambitious and high-spirited, dreaming of developing huge oil fields and serving the country. However, countless exploration operations have ended in failure. Therefore, the headquarters issued an order to evacuate the mining area. The headquarters sent Captain Zheng Wan (played by Ahn Sung-ki) to persuade everyone to evacuate. Because his father had been buried on the seabed, the equipment manager Jun Hai (played by Ha Ji-won) did not want to disappoint his father and leave. She firmly believed that there was oil on the seabed, so she refused to obey the evacuation order. The headquarters issued an ultimatum that all crew members must organize and retreat within one month. When Jun Hai and the crew were making the last attempt at oil exploration, suddenly, the signal to contact the headquarters was interrupted. In panic, the crew felt that something was lurking in the sea, and a strange and terrifying atmosphere enveloped the "Eclipse". Then, the people on the ship died one after another strangely...