Nothing is certain in director David Twohy's creepy submarine thriller. The captain of World War II sub U.S.S. Manta has died under dubious circumstances, and the crew is already on edge when they rescue three survivors of a torpedoed British hospital ship. When one of these survivors is a woman (Williams), allegedly unlucky on a sub, tensions run even higher. With the Germans tracking the sub, strange events begin to occur, which could be vengeful actions of the captain's ghost, a saboteur, hallucinations caused by lack of oxygen or some combination of the three. As the disasters pile up, the crew becomes divided between acting captain Brice (Greenwood) and rebellious ensign O'Dell (Davis), who has the strangely outspoken Claire on his side. Characters are a bit one-dimensional, but the effects and acting are above average for a B movie.