A group of U.S. Navy engineers, led by Capt. Laidlaw (Taurean Blacque), are building an underwater base when they inadvertently disturb the lair of a gigantic creature. The monster attacks, and the crew, including lovers Collins (Nancy Everhard) and McBride (Greg Evigan), tries to evacuate, but the facility is badly damaged. After the exterior is breached, the increasingly desperate people become separated from one another, and the creature begins to pick them off one by one.