A group of employees working for the oil company Vaxxilon are working on a boat in the Indian Ocean off the coast of Somalia. One night a boss, Karsen, sends four of his men, Engel, Mitchell, Jones and Hurst, down in the diving bell to fix a damaged oil pipe. Having completed the work they make the ascent but the support ship is hit by a storm, causing the cables holding the bell to break.

Desperately trying to make contact with the ship, one of the crew members goes out to assess the damage, only to find the body of Karsen and the wreck of the supply ship on the bottom of the ocean. The four men then have to use their wits and knowledge of diving and the bell to try and escape from the ocean floor, 670 feet (200 m) down, with a limited oxygen supply.