At a Pollard Underwater Center diving platform, Danny Murray is planning to check out reports of mysterious late night divers. He's using an experimental suit designed by Henry Pollard, who tells Danny to be careful. However, after Danny goes down, Pollard flips a secret switch and Danny's suit overpressurizes and explodes, killing him.
Ray meets with Danny's wife Annie, an elementary school teacher. She wants him to investigate Danny's disappearance, explaining that Danny commuted to work at the Pollard Center and only met with his wife and son on weekends, but missed his son's birthday. During the week Danny stated at a rented apartment near the Center. Now the Pollard Center denies that Danny ever worked there. Ray takes on the case and applies to the Pollard center with a fake ID showing him to be an ex-Navy diver. Pollard shows Ray around the Center and talks about his projects like their dolphin training center and a power research project. They meet with Karen Marshall, a dolphin researcher who Pollard causally hits on. Ray agrees to take the job.
The end-shift bell goes off and the staff leave under the careful scrutiny of an electronic system that monitors their badges. Ray checks out the security and then goes to Danny's apartment. He finds Karen there, covering her tracks: she was having an affair with Danny. Ray says he's Danny's friend and trying to locate him, and Karen is puzzled since she knows Danny worked there. As they talk, Ray walks by the active radio and his badge sets off a burst of static, indicating it has a transmitter inside. Ray tells Karen that Danny was married and Karen laments that she always gets involved with the wrong kind of man. She also admits that Pollard keeps hitting on her but she has no choice but to accept it so she can keep her job.
That night, Pollard orders his security chief Frank Gallagher to check out Ray's background. Meanwhile, Ray sneaks into the compound using a security badge. He's instantly detected by the security team and they send out a patrol to bring him in. Ray moves through the compound and enters into the underground tunnels, which contains hundreds of pipes. He also sees two divers who are coming back from an after-midnight dive. The security chief sees Ray seemingly go into a dead-end room, only for the guards to discover Ray left the badge there. Ray, meanwhile, has made it to the locker room where he finds a ruptured suit that belonged to Danny. He then gets out through a surface hatch and escapes from the grounds.
The next day, the security team arrests the man with the intruder's badge: one of Ray's co-workers. Ray stole his badge and used it the previous night. Pollard continues to check Ray and goes to the chamber where he's undergoing tests in a pressure suit. Pollard increases the pressure in the suit, threatening to rupture Ray's ears if he doesn't answer correctly. Pollard then asks Ray questions fro his dossier and Ray manages to answer them all correctly despite the pressure.
That night, Ray meets with Karen and they chat on the beach. He's figured that Danny was involved in something dangerous and Pollard is up to no good. Karen complains that no one takes her seriously because of her beauty and the two end up kissing.
The next day at the end of the shift, Ray slips his badge into a woman's purse so it appears that he's left the facility. He then slips into the tunnels and traces the excessive piping and locates a facility that Pollard is using to transport stolen oil.
Gallagher discovers that Ray supposedly died in 1945 during World War II in the Pacific. Pollard refuses to dispose of Ray for the moment, insisting they need to find out what he knows. Gallagher complains that Pollard's plan to destroy the drilling rig they're stealing the oil from will kill dozens of men but Pollard dismisses his concerns, warning Gallagher he knew what they were getting into.
Ray and Karen go out on the ocean and Ray goes diving to trace the pipes and find out where Pollard is stealing his oil from. Karen wonders what will happen between them once Ray has solved the case, but he says he can't promise her anything. He discovers that the pipes go out to the oil rig and returns to the boat... only to find Pollard waiting for him. Karen betrayed Ray in return for a position at the Center.
Pollard takes Ray back to the Center and locks him in a decompression chamber, then increases the pressure so that opening the door will instantly kill Ray. The chamber has scanners that monitor Ray's telemetry at all times. Pollard then leaves, preparing to go out to the rig with two of his men and use five-minute explosives charges to destroy the rig and cover his theft.
Ray outwits the system by using a yoga technique to slow down his heart. The technician monitoring the telemetry restores the chamber to normal pressure and goes to investigate, and Ray regains consciousness and knocks him out. When Gallagher sounds the alarm, Ray hides in Pollard's office where Karen finds him and offers her help to escape. He wonders at her change of heart and she admits that he's been causing her to question herself. Ray wants her to help him get to the rig and save the men and she reluctantly agrees.
Ray uses a self-propelled motor to get out to the rig where Pollard and his men are already working. Ray takes out the other two men and takes on Pollard. Grabbing one of the explosive charges, Ray attaches it to Pollard's dive tanks and swims away. Pollard tries to remove it but the explosion goes off away from the rig, killing the man.
Back on land, Ray finds Karen trying to escape. He takes her car keys and warns her that she played a part in Danny's death, and doesn't get to walk away from it. He departs as the police arrive to take her into custody.
Ray meets with Angie after lying to Eric about how Danny died. Annie notes that she's noticed that Ray tends to glance down when he's lying, which she finds comforting. Then she asks him if Danny was having an affair. Ray looks her straight in the eye... and lies. Convinced, Annie goes to introduce her son Eric to Ray. When they return, they discover that Ray has already slipped away, his mission accomplished.