A U.S. Naval fleet is out on the ocean, tracking something coming down. They're unable to identify it, although there is a Russian satellite overhead in the vicinity, and it hits the water and goes down. A deep-water recovery ship, Pearl Harbor, moves in and a private organization, INTERSECT, supporting the Royce salvage team, is authorized to use any research vessel necessary to recover the object.
Nearby, a Russian sub receives orders to prevent the Royce team from recovering the object.
Leonard Driscoll, head of the INTERSECT support group, arrives and reports that he's missing one of their men, Special Agent Sam Casey. He's flying air/sea rescue, and Leonard meets with Royce executive director Dr. Harold Schuyler and Charles Edward Royce. Charles tells Leonard that Sam has gone fishing in a helicopter
Sam's helicopter hovers above the ocean and he watches the sharks circling in the water beneath him. He's lowered a winch with bait on it, and one of the sharks goes for it. It takes the bait and Sam is unable to reel it in. His friend Dr. Abbey Lawrence is watching from the nearby ship, while the man with her, Vince Rogers, complains that Sam is going to put the chopper in the water. Leonard radios Sam, who says that he's handling business by eliminating sharks in the waters. With ten minutes to dive, Sam heads back.
When Sam arrives at the conference room, the drive officer is briefing the divers on the water conditions. Charles then takes over and explains that the mass shifted ten minutes ago, messing up the configuration, and introduces Leonard. Leonard tells the divers that it's supposedly a Russian weather satellite but Fleet Intelligence figures that it's an atomic-powered laser. The Royce team will go down first and secure the cables, and then Sam will go down last and make sure everything is hooked up properly.
As the divers gear up, Harold gives the Royce head diver, Vince Rogers, a small mine and says that it has a four-minute timer. Vince wonders what will happen to Sam, and Harold admits that his death can't be helped. The four Royce divers go down to the satellite. Meanwhile, Harold notices that Charles is a little short of breath. Charles goes to his cabin to catch his breath, and Leonard asks if he's all right. Harold says that it's angina brought on by tension. Leonard wonders if Harold runs the company, and Harold assures him that Charles is the man in charge.
The divers reach the satellite and attach the cables. Vince secretly places the explosive charge on the satellite and activates it. On the ship, Sam gears up and heads down to the satellite. He confirms that they hitched up a sling and passes the Royce drivers going up. Once they test the sling, they start winching it up. Sam spots the timer on the mine moving, just as the mine goes off. The techs on the ship detect high levels of radiation, and Harold warns that they can't risk sending the divers back. Abbey warns that the chances of Sam surviving are zero, and Leonard bring up the safety cable hoping that Sam is still attached to it.
Leonard has Abbey ready the two radiation suits and she and Leonard enter the decompression chamber. They confirm that Sam is still alive but unconscious, However, when they remove his faceplate they discover that Sam is invisible. The wetsuit turns invisible as well, and Abbey's hand turns invisible as she touches Sam. They apply a respirator and stabilize Sam, and Leonard says that they'll wrap him in bandages to keep his condition a secret.
The crew brings the bandaged Sam out and places him in a portable decompression chamber, and then loads him aboard the INTERSECT helicopter. When the helicopter arrives at INTERSECT, Lawrence and Abbey take Sam to the main la .Abbey confirms that Sam is getting weaker and figures that the invisibility is draining him. She and Leonard put on a breastplate to keep Sam's heart going, and Sam wakes up. They explain where he is, and Sam can't remember what happened before the bomb went off. His friends tell him that he's fine and to get some rest, and they leave.
Once he's alone, Sam gets up and removes the bandages from his head. Once he sees what has happened, he yells and Abbey and Leonard run back in. They tell him what happened: the radiation distorted Sam's DNA structure. Sam wants to know if it's permanent, and Abbey admits that they don't know yet.
At Royce Industries, Charles tells Harold and Vince that Sam is still alive according to Leonard. He says that there's been no report yet on what caused the explosion and leaves. Vince insists that Sam couldn't have survived the explosion. He admits that if Sam had seen the mine, he would know what it is. Harold says that they have to get in to see Sam, and he'll work it through Charles.
Abbey continues to run tests on Sam, who insists that there is a stability factor. He suddenly weakens and she calls Leonard in. They apply a stabilizer device to his arm and remove the breastplate, and Sam flatlines. His body then builds up a counter -field against the invisibility and they apply a cardiac booster to revive him. Sam reverts to visibility and his heart starts beating, again, He wakes up and Abbey confirms for him that he's visible again.
As Sam eats, Abbey tells him that as long as he stays hooked up to the stabilizer. However, she warns him that without the machine, he fades out permanently. Leonard tells him that he's working on a miniaturized version, and Abbey calls for the miniaturized unit.
Charles, Harold, and Vince arrive at INTERSECT. Charles tells Harold to get to Sam and find out what he saw. Leonard is called away to meet with Charles, and Abbey gives Sam the miniature stabilizer. It looks like a digital watch, and Abbey assures him that it can't run down because it's powered by an atomic battery. He can turn it on and off, but it has to stay in contact with his skin or he has to hook back up to the stabilizer.
In Leonard's office, Charles tells Leonard that the SIA intercepted a message from Russian Intelligence that someone in the salvage is a saboteur. He convinced the State Department that they would handle it internally, but they figure that Sam is the saboteur and accidentally blew himself up. Leonard points out that the SIA gave Sam an honorable pink slip and let him go because they couldn't cope with him. He says that each of them should investigate their own crew and then compare notes, and Charles agrees. As he leaves, Charles admits that he sent Harold and Vince in to question Sam behind Leonard's back, and he'll call them off.
Abbey puts on a monitor unit disguised as a matching wristwatch. She shuts down the main stabilizer and Sam stays that he feels great. He immediately turns the device on and off, flickering in and out of visi8bility. Sam says that he has to work harder when he's invisible, and Abbey figures that he has a time limit.
They hear someone outside and assume that it's Leonard, and Sam turns invisible. It's Harold and Vince, who ask to see Sam. Abbey says that he's at the x-ray facility and they explain that they want to take him with them and administer pharmaceuticals. Leonard and Charles arrive and Charles leaves with his men. Once they're gone, Sam says that he can't turn the stabilizer on and collapses. Abbey finds him and turns it on, and tells Leonard that Sam is too weak and has to work up to the time limit. She figures that Sam can only stay invisible for 15 minutes a day. At 16 minutes, he passes out and fades away, and never comes back.
As they talk, Sam gets a memory flash of seeing the mine on the satellite. He finally remembers what he saw and identifies it as a magnetic mine, type R-3. The R-3 was made by Royce. Leonard insists that Charles is a patriot, and warns that they have no proof. Sam says that he'll go in and get some proof, using the code name Minus One. Abbey agrees with him, and Leonard reluctantly says that they'll turn Sam loose the next day.
The next day, Sam tells Leonard and Abbey that he's heading to Royce. He takes his motorcycle while Abbey and Leonard take Abbey's jeep. Sam speeds off and Abbey races him, and a highway patrolman spots Sam going by. He turns on his siren and drives after Sam, and Sam finally pulls over. Sam then goes invisible as the officer arrives, and Leonard and Abbey drive by. The officer checks the seemingly abandoned motorcycle and then goes into the nearby woods to find the driver. Sam lets the air out of the patrol car's tires, reverts to visibility, and takes off again. The officer hears the engine and comes back, but his car isn't going anywhere.
Abbey and Leonard arrive at Royce Industries and find Sam waiting for them. They know what he's done and how much invisibility he's used via Abbey's monitor, but Sam assures them he still has plenty left. They go inside and Charles, receiving word that they're there, notifies Harold and Vince. When they meet in Charles' office, Sam explains that he saw the R-3 attached to the satellite. Charles tells him that the SIA believes that Sam planted it, and Leonard points out that Sam couldn't have intercepted the coded message without being detected. He insists that it was a member of the crew who had the authority to use the radio equipment without raising suspicion, and warns that every member of the dive crew is under suspicion. Charles takes a pill for his angina and has his head of security, Captain Whelan, send in some guards to escort the trio off of the property.
As they leave, Sam tells the others to go ahead, turns invisible, and says that he's going to poke around. Abbey warns that it's too dangerous, but Sam insists that he'll just use the invisibility to sneak past the guards and will meet them later. Whelan and his men arrive and wonder where Sam is, and Abbey claims that he went on ahead. Whelan looks around, going back to Charles' office, and Sam slips in through the open door.
Once Whelan leaves, Charles says that they'll have to investigate every man who had access to the radio. He insists on doing it personally, but Harold warns that Leonard will try to divert suspicion from Sam. He suggests that Charles let the State Department know in person, guaranteeing containment and protecting the company. Charles agrees, and Harold and Vince leave to order the plane.
At the hamburger stand where they agreed to wait, Abbey realizes that Sam has used five minutes of his invisibility.
Sam reverts to visibility and comes up behind a receptionist, Gloria Dixon. He asks to see Harold and she gives him directions while flirting with her.
Harold and Vince return to Harold's office and the doctor calls Taggart, the executive jet pilot. Meanwhile, Sam slips invisibly into the office. Meanwhile, Whelan continues his search and sees Sam just as he comes out. Sam reverts to invisibly again, avoiding the guards, turns visible when they pass, and heads out. A guard, McNeil, spots him and chases after him, and Sam turns invisible again to duck the man. He drives off in a van as Whelan arrives, heading to flight operations.
Sam drives to Charles' jet with the security guards in pursuit. They finally corner Sam in a hangar, and he turns invisible to escape. Outside, Sam turns visible and goes to a locker room. He finds a set of mechanic's coveralls and puts them on.
Abbey and Leonard wait, and figure that Sam is onto something.
Taggard picks up his flight papers and goes to the jet, and Sam checks the orders slot to discover where he's going. He then drives a luggage cart to the jet and tells the mechanic that he's delivering food for Charles. The mechanic says that it only has enough fuel for Denver, not DC, and it's a routine flight to check the oxygen system. Sam drives back and uses a truck's portable phone to call Abbey's car phone. He tells them that Charles is in danger, figuring that the change in oxygen when the plane flies to Denver will bring on cardiac favor. A guard comes over to the truck and an invisible Sam is forced to leave. Leonard figures that Harold is making deals with enemy powers behind Charles' back, and if Charles dies than Harold gains control of the company. He and Abbey drive off.
The guard has the operator trace the call on the truck phone, while an invisible Sam drives off in a nearby car. He goes back to the main building and barges into Charles' office, and Charles calls security. Sam warns him that the preflight checklist shows the jet has been serviced for a trip to Denver and they're planning to kill him. Whelan and a guard arrive and drag Sam off. Once Charles leaves, Sam attacks the guards and fights his way out. He runs back to Gloria and tells her to close her eyes. Once she does, Sam turns invisible and when the guards arrive, Gloria has no idea where Sam went.
Charles boards the plane with Harold and the others.
Sam runs to the jet just as Abbey and Leonard arrive. Over the jet engines he can't hear Abbey warning him that he only has seven minutes of invisibility left. Turning invisible, he gets into the planet just in time before it lifts off and hides in the lavatory.
In the cockpit, the co-pilot tells Taggart that he fixed the flight record so it shows that they took off with a full load.
After talking with Charles, Harold and Vince meet with their men and say that they're going to thin out the oxygen. Taggart will say over the intercom that they're at 38,000 and then they should put on the air masks.
In Charles' office, Sam turns visible when he's not looking and offers him several pills for his heart. He convinces Charles to hear him out, and repeats the conversation Charles and Harold had earlier. When Charles wonders how he heard the conversation, Sam demonstrates his invisibility and explains what happened to him. He tells Charles about Harold's plan. There's a knock at the door and a man checks on Charles. Once he leaves, Sam reappears and thanks Charles for not turning him in. He tells Charles to stay there, fades out, and goes into the next cabin.
Leonard calls for police and ambulances, and Abbey reports that Sam only has four minutes of invisibility left.
An invisible Sam gets a portable oxygen tank from the first aid kit. Holding it low, he carries it past Harold and the others and into Charles' office. The plane reaches 38,000 and Sam and Charles don masks. Harold and his people do the same. Vince goes to check on Charles and sees him with Sam, closes the door, and sounds the alert. However, when he goes back in, Sam invisibly knocks them back and locks the office door. He then comes out and yanks out their air hoses, and tosses Taggart out of the cabin and locks the door. Vince tries to shoot it open and the ricochet hits a window, shattering it. The cabin violently depressurizes
Sam takes control of the plane, levels it off, and takes the plane down to a lower level. He calls Charles on the intercom and has him tie up the unconscious conspirators, and then fades out as the stabilizer malfunctions.
Abbey sees the malfunction on her monitor but doesn't know what is causing it.
Sam fades in and out and finally stabilizes into invisibility. He then sends an SOS out, and the chief controller at LAX talks him through heading back to Royce Industries' airport. Sam starts to fade out again and has the controller call Abbey.
Harold and the others wake up and realize that Charles has tied them up. Charles calls to Sam through the door, and Sam tells him to belt himself in. Sam fades out entirely as the controller patches Abbey in. She warns that she can't tell how much time Sam has left, but it's less than two minutes based on the last readout.
Royce Tower takes over and Captain Ballard on the runway takes over. He talks Sam through bringing the jet down, while Whelan receives orders to let the police, ambulance, Leonard, and Abbey in. With Ballard's help, Sam brings the plane down safely. The monitor shows zero seconds left, and Abbey and Leonard run aboard and go to the cockpit. Abbey repairs the stabilizer and they put it back on Sam, and he turns visible. He confirms that he's okay and they leave.