In Washington, D. C., United States Navy Lieutenant Commander Tom Farrell attends a presidential inauguration ball where he meets Susan Atwell, who indicates that she is the mistress of one of the high-powered officials in attendance. The two are drawn to each other and leave early, but go to her friend Nina Beka’s apartment to have sex because Susan cannot risk her lover finding him in her apartment. The next day, Susan drives Tom to the airport and kisses him goodbye. Based on a battleship, Tom rescues a crewman who falls overboard during a storm, and is hailed a hero by the media. Defense Secretary David Brice reassigns him to the Pentagon in Arlington, Virginia, to be his liaison with the intelligence community. Brice explains that the military has spent $2 billion over five years on a failed prototype for a huge “phantom submarine” undetectable to sonar. Brice intends to terminate funding for the project, but knows he will get resistance from Congress, especially Senator Duvall. Anticipating Duvall to cite facts from Central Intelligence Agency (CIA) reports that support continued funding, Brice asks Tom to obtain copies, so he can refute Duvall’s arguments. Tom visits Susan’s apartment and resumes his affair. When she takes a Polaroid photograph of him, he pulls the paper off too soon and it does not develop properly. Noticing Susan’s expensive gold jewelry box, he assumes her high-powered boyfriend bought it for her, but she claims it was originally a gift to him from a foreign government. Pressed to identify her lover, Susan reveals it is David Brice. As she prepares to go to a black-tie party, she explains that Brice will be there with his wife, but he enjoys seeing Susan waiting in the wings. Tom becomes jealous, crashes the party, and sneaks away with Susan before Brice can get her alone. They drive to a bed and breakfast along Chesapeake Bay for an idyllic romantic weekend together, registering under the name Mr. and Mrs. Smyth. While sailing on the bay, Susan declares her love for Tom. However, when they return to her apartment in Washington, D. C., Tom is angry that he has to share her with Brice. Seeing Brice arrive, Susan hurries Tom out the back door, but Brice sees his figure hurrying away in the dark. He accuses Susan of cheating, and slaps her. Susan falls over a railing onto the dining room table below and breaks her neck. Brice confesses to his assistant, Scott Pritchard, with the intention of surrendering to police, but Pritchard convinces him to instead return to Susan’s apartment and clean up any evidence that links him to her. Pritchard concocts a scheme in which they will claim that a mythical Russian spy named “Yuri,” long rumored to be in American military intelligence, has infiltrated the Pentagon, and was having an affair with Susan. Accusing Yuri as the one who killed Susan, they will conduct a massive manhunt for him. Brice and Pritchard assign Tom to head the search for Yuri. When they give Tom the file, he realizes Susan is dead. When Tom demands more details for his investigation, Pritchard reveals that Susan was the mistress of both Brice and Yuri, and the news linking the Secretary of Defense to a Russian spy would create a national scandal. Meanwhile, the Pentagon’s Criminal Investigation Division (CID) goes through the evidence collected at Susan’s apartment and finds the poorly developed Polaroid photograph. Computer technician Sam Hesselman, an old friend of Tom Farrell’s, says a computer program can enhance the image, but it will take many hours. When Pritchard and Tom question Susan’s friend, Nina Beka, she admits Susan was seeing Brice, but keeps quiet about Tom. Afterward, Pritchard sends two U.S. Army Special Forces assassins to silence Nina. Tom races to stop them and sends Nina away before they can kill her. He slips Susan’s gold jewelry box out of the evidence bag and sends one of his men to translate the Arabic inscription on the box. Meanwhile, Tom has Sam Hesselman check State Department records to see if Brice registered the jewelry box as a gift from the Moroccan government. Sam prints a long list of gifts given to United States officials from foreign governments. Investigators track down the man who rented Tom the boat in Annapolis, Maryland, and bring him to the Pentagon. He spots Tom from a distance, but Tom rushes away before he can be identified. Officials seal the building and take him room to room looking for the man he pointed out. They also bring the bellboy from the bed and breakfast to the Pentagon and join the search. As Sam’s computer enhancement of the Polaroid photograph progresses too quickly, Tom confides that Pritchard is trying to frame him and asks his friend to slow process to give him more time to prove his innocence. When the printout of gifts to government officials shows Brice did not register the gold jewelry box, Tom asks Sam to insert evidence of the gift into the computer records. Sam agrees to both requests, but later tells Scott Pritchard that he believes Tom is in over his head. However, when Sam reveals that Tom suspects Brice killed Susan, Pritchard shoots and kills him. Tom goes to Brice, demanding the search be ended immediately or he will show the CID that Susan’s gold jewelry box was a private gift from the Moroccan government. Seeing the computer printout, Brice knows Tom has trapped him. Pritchard comes to Brice’s office announcing that “Yuri” has killed Sam Hesselman, but Tom realizes Pritchard is the murderer. Brice suggests to Tom that they accuse Pritchard of being “Yuri” and the one who killed Susan. Distressed that Brice plans to betray him, Pritchard picks up a gun and shoots himself. Brice tries to make a deal with Tom to keep his secret, but Tom remains noncommittal. He goes to a suburban house to be debriefed about the incident. Afterward, a Russian KGB agent appears and congratulates Tom for his deep undercover mission infiltrating American military intelligence, but tells him it is time to return to Moscow. Tom refuses, rushes out of the house, and drives away.