At a cocktail party at the Reisner Institute, a Washington think tank, an invisible force drags a scientist named Devin (John Shaw) into a nearby bathroom, where the force (implied to be a person) brutally throws Devin around for information. Devin mentions another scientist, Maggie Dalton (Laura Regan), who knows the "formula" the invisible person is looking for. Apparently accepting this, the man releases him, warning him not to divulge information about this incident to anybody. As soon as the invisible man leaves (or rather, pretends to leave), Devin attempts to call someone on his cell phone, but the invisible man smashes the phone and slashes Devin's throat. The police arrive at the laboratory to conduct a murder investigation, but the laboratory's military supervisor, Colonel Gavin Bishop (William MacDonald), insists it is an internal military incident and the police have no jurisdiction. Fearing attacks on the remaining scientists, the lab's owner, Dr. William Reisner (David McIlwraith), employs Frank Turner (Peter Facinelli) and his partner, Detective Lisa Martinez (Sarah Deakins), to protect Maggie, but refuses to divulge any information on the nature of his work.The two detectives stand guard outside Maggie's house (where she lives with sister Heather Dalton (Jessica Harmon)). When Lisa opens the door to let the cat in, the invisible man sneaks past her into the house. Just as he reaches the study where Maggie is, Lisa tracks him down, and he strangles her with a lamp's power cord. Suddenly, armed military commandos appear and storm the house, using thermal goggles to target and corner the invisible man. Outside, Turner confronts Bishop, realizing that they used him and Lisa to lure the invisible man to the house. Several stun grenades go off around the house, incapacitating the soldiers and allowing the invisible man to escape in pursuit of Turner and Maggie. He almost catches up to them, but is struck and badly injured by a car, and flees. The invisible man is shown to be taking regular injections of a serum that keep him invisible.Maggie is taken into protective custody by the police, where Turner's superior and friend, Captain Tom Harrison, has received orders to have her transferred to military custody. Frank helps Maggie escape from the police station, and they flee in a stolen car. Bishop and Reisner, knowing their careers would end if Maggie talked, and declare them fugitives.Maggie later tells Turner that five years prior, a team of scientists figured out how to make humans invisible, but something went wrong, leaving only two survivors. A year after the original project was scrapped, the Reisner Institute restarted the experiments as a covertly Department of Defense-funded operation to create the perfect soldier, code-named "Silent Knight", which attempts to render humans invisible. The resulting serum does turn human tissue invisible, but with adverse effects: as it allows light to pass directly through the subject, the radiation damages the cells and causes physical and mental degradation, slowly killing the person. Maggie developed a compound called the "Buffer" to counteract the effects of that particular radiation. A soldier named Michael Griffin (Christian Slater) volunteered, and the serum succeeded, but the Buffer failed, and Griffin seemingly died, which in turn got Maggie fired. Maggie believes that Griffin faked his death so he could use his powers without restraint, but now needs the antidote to the radiation before he dies.Maggie receives a message from a man named Ludlow, who has been in contact with her for weeks. Turner uses his contacts to find Ludlow, a soldier enlisted into the program after Sebastian Caine (Kevin Bacon) (the original guinea pig), but before Griffin. He had gone into hiding but is now slowly dying from radiation. Ludlow has also been tracking Griffin and reveals the true story to his supposed "death" and the program itself: Operation Silent Knight was never about national security, and neither was Griffin given the Buffer, since the Department used him to assassinate their political enemies.Meanwhile, Griffin infiltrates Bishop's office and both get into a fight. The latter attempts to reason with him and then, getting desperate, stabs him, but not kills him, with a pen. Griffin impales Bishop with the same pen and uses his computer to locate Ludlow. Arriving at the hideout, Griffin attacks Turner, but Ludlow intervenes, sacrificing himself to allow Turner and Maggie to escape. Griffin decides to make them return by capturing Maggie's sister. When they meet at the train station where he is hiding, Griffin silently catches Maggie and tries to turn her invisible so he can take her unnoticed, but Turner intervenes. After a short fight, Griffin escapes with Maggie, leaving Turner with the arriving Reisner and his guards. A short time later, Reisner pursues an invisible man, but is soon captured and held by him. Believing him to be Griffin, he offers to send for the Buffer. The figure, however, is Turner, who used Griffin's discarded syringe to become invisible as well. Reisner, backing away, is hit and killed by a speeding car.Griffin takes Maggie to her old college laboratory to create the Buffer for him. Griffin forces her to inject herself with it first, then injects himself with another dose. With his survival seemingly assured, Griffin tries to kill Maggie, but Turner (now invisible) intervenes and knocks him out of the laboratory window. Turner runs outside, where Griffin renders him unconscious. As Griffin slowly turns visible, Maggie reveals that he has been poisoned, as the vial contained rat poison; she loses consciousness as she has been injected with the same poison. Enraged, Griffin takes a shovel and attempts to kill her, but Turner, having recovered, stops him and impales him with the shovel. He then carries Maggie away for medical attention, leaving Griffin's body outside in the rain.A few days later, Maggie is recovering in hospital and is poised to be released. Heather tells her that Turner has not been found. Maggie insists that he will come back to her, as she knows that he needs her. Outside, they are being watched by a hooded invisible man, presumably Turner, who then walks away.