Directed by George P. Cosmatos, Leviathan deals with the perils of an ill fated undersea mining operation. As the film opens we meet Miss Martin (Meg Foster), the CEO of Tri-Oceanic Corp., she hires a geologist named Steven Beck (Peter Weller) to supervise an undersea mining operation for six months.
Beck soon meets his crew: Dr. Glen ‘Doc’ Thompson (Richard Crenna), Elizabeth ‘Willie’ Williams (Amanda Pays), Buzz ‘Sixpack’ Parrish (Daniel Stern), Justin Jones (Ernie Hudson), Tony ‘DeJesus’ Rodero (Michael Carmine), Bridget Bowman (Lisa Eilbacher) and G.P. Cobb (Hector Elizondo).
Once the assignment begins the crew begin their expected work. One day, whilst working outside their deep sea station in a pressure suit, Sixpack discovers a Soviet shipwreck, Leviathan. The crew salvage a safe from Leviathan, finding records detailing the deaths of several crew members as well as a video log from the Captain (Eugene Lipinski). Sixpack also finds a flask of vodka which he drinks with Bowman.
Doc and Beck examine the Captain’s video, which reveals bizarre medical problems amongst the Leviathan crew. They also discover that Leviathan was deliberately sunk/scuttled.
The following morning, Sixpack feels sick and Doc discovers lesions along his back. He dies a few hours later, but Doc and Beck keep it quiet to avoid a panic. Doc checks the crew to confirm no one else is sick, but does not have the chance to examine Bowman.
Later, Beck and Doc confer with Martin on the surface and Bowman begins feeling ill. She finds Sixpack’s corpse, which is mutating and growing. When Bowman’s hair starts falling out, she realizes the same thing is happening to her. Realising that something bad is about to happen, Beck and Doc request emergency evacuation, but Martin reports a severe storm on the surface that will delay evacuation for 12 hours…