16,000 feet below the Atlantic Ocean a team of miners finish the eighty-seventh day of a ninety-day mission, when DeJesus’s suit malfunctions and loses air. Beck, the team leader, orders the miners to rush DeJesus to the habitat module. His next call to “Doc” for medical aid goes unanswered, but DeJesus gets aboard just as his suit runs out of oxygen. Later, the crew’s resentment against Doc grows when he joins them in the mess hall and does not apologize for not being at his station during the crisis. To prevent a mutiny, Beck tells the crew if they do some light maintenance on the habitat, they can have the next day off. “Sixpack,” a redneck drill jockey, plants a crab in DeJesus’s suit to scare Willie, a British woman, when she repairs it. He is chastised by Bowman, a red headed woman, who orders him to clean the day room. Down in the engine room, Cobb, an older mechanic, shows Jones, another drill operator, how to fix the carbon recycler with chewing gum. Beck calls topside to talk to Martin, a high powered female executive who insists Doc is a qualified researcher although a serum he developed killed some people. Beck turns down her offer to talk to Doc about his lax attitude. The next day, Sixpack is drilling when he falls off a cliff and loses radio contact. Willie goes after him, and discovers a sunken ship named Leviathan. Bowman runs the name through the computer to learn the ship is listed as being on active duty in the Baltic Sea. Willie pushes on and discovers Sixpack carrying a safe and proclaiming his new-found wealth. Onboard, the crew opens the Leviathan safe to find a videotape of the Captain’s log, a flask of vodka, which Sixpack steals, and files marked deceased. As Beck views the videotape, Doc translates the Russian Captain reporting his whole crew is down with a strange disease, but the tape cuts off before he can give any details. Later, Sixpack and Bowman share the stolen vodka. The next day, Sixpack reports to sickbay where Doc discovers Sixpack’s skin is becoming scale-like. Beck calls Martin to request a medical evacuation, but after being informed that an early departure will be a black mark on his record, he decides to wait for their scheduled pick-up. In sickbay, Doc takes a skin sample from Sixpack and discovers his cells are mutating. He sends his findings topside to a Naval hospital, and learns that this is an unknown disease. After Sixpack dies, Doc and Beck teleconference with Martin and demand immediate evacuation, but she tells them a hurricane is nearing, preventing pick-up for at least twelve hours. Not wanting to alarm the crew, Doc and Beck keep Sixpack’s death a secret. Meanwhile, Bowman gets so sick that Willie and Jones carry her to sickbay. They go to find Doc, leaving Bowman to discover her skin is also becoming scaly and her hair is falling out. She goes to see Sixpack and finds his dead body mutating into a monster, then she runs into a shower and slashes her wrists. Beck finds her body and puts it with Sixpack’s. He calls a conference to explain about the hurricane. Hearing glass breaking in sickbay, Doc and Beck rush to find both corpses have merged and are further mutating. Fearing contamination, they put the bodies into a body bag and have the crew carry them to the airlock. A claw rips open the bag and scratches Cobb. They hurl the bodies into the airlock and slam it shut, but a deformed leg is chopped off and falls unseen onto the deck. It rolls into a desalination unit where an eel-like creature wiggles out of the severed limb. After Doc and Beck view footage of the sunken ship, they realize the crew’s skeletons are malformed. Doc suggests the Russians were conducting genetic experiments to create humans who could live underwater. Later, DeJesus and Jones are in the mess hall when the creature leaps from an overhead compartment and chews its way into DeJesus’s chest. Jones rushes out of the room and activates the airlock. He returns with Doc and Cobb to discover the monster has chewed through a steel door. Then the lights go out. After finding Willie, Beck explains everything to the crew. Doc reports that the creature has eaten their blood supply, which means the creature is growing and getting hungry. Also, the fact that it knew where the blood supply was indicates it absorbs its victims’ memories. Armed with power saws, drills and flamethrowers, the crew searches for the creature. Doc and Cobb see sparks coming from a cable box. Cobb puts his saw down to fix it and the monster latches onto his leg. Doc cuts it in two with a saw, but both pieces wiggle away. Realizing they cannot escape, Beck decides to set a trap. He has Doc take blood from each of the crew, then he and Jones, armed with flamethrowers, smear a trail of blood to the dive platform at the outer airlock. Doc leaves Willie and Cobb, claiming he is getting bandages for Cobb’s wounds, but he goes to the bridge and releases the escape pods. He returns to Cobb and Willie to discover Cobb’s chest has something inside it. Cobb lifts his hands to reveal teeth growing in his palms and attacks Doc as Willie escapes. In a passageway she sees the first monster, which has become a biped with multiple arms. Before she can scream, Beck yanks her into a suit room. Realizing there are two creatures, Beck decides to abandon ship. He, Willie and Jones rush to the bridge and discover a message Doc sent to the company stating he released the escape pods to contain the disease and for them not to attempt a rescue. Beck calls Martin who claims the hurricane has worsened and it will be another forty-eight hours before they can be rescued. Beck attempts to check the weather report, but the computer denies him access. Willie pulls up a news report that lists the crew names as deceased due to an underwater accident. Alarms go off and a computerized voice states pressure is dropping and implosion of the complex will occur in ten minutes. Finding the main air vent damaged, Jones tells the crew their only chance is to use the diving chamber’s air supply. As they make for the airlock, one of the creatures attacks. They burn it to death with the flamethrowers. Another appears, but dripping water has extinguished both flamethrowers, so Beck rips out two wires and electrocutes the monster. The habitat begins to break up around them, as another creature, which still has Doc’s face, grabs Beck. Beck uses a saw to cut off its arm. Finding they are unable to reach the air valves, Beck orders Jones and Willie to get into their diving suits, then attaches floats to their suits. Another creature arrives wearing DeJesus’s face. Beck hits the button to lower his crewmen into the ocean, then pours flammable liquid onto the floor, lighting it with a flare. As the creature battles the blaze, Beck gets suited, and lowers himself outside the module seconds before it implodes. Upon reaching the surface, the three survivors find sunny skies. They fire a flare at a Coast Guard helicopter. As the airship descends, the DeJesus creature breaks the surface and kills Jones. Beck hurls an explosive into its jaw and it blows up. They are flown to an oil rig where Martin greets them. When she claims she knew Beck would survive, he punches her in the face and walks away with his arm around Willie.