Frank Horrigan (Clint Eastwood
) is a Secret Service agent who is close to retirement age. When the story opens, he's waiting for a pickup from his new partner, Al D'Andrea (Dylan McDermott
). They drive to a marina just outside of Washington DC to meet with a counterfeiter, Mendoza (Tobin Bell
). Frank and Al are posing as buyers of false currency. Mendoza asks Al to board his yacht; after Al leaves, Mendoza reveals to Frank that he's been suspicious about Al, and figured out that Al is a Secret Service agent.
When Frank boards the boat he sees that Mendoza's thugs have bound and gagged Al. Mendoza wants Frank to shoot Al as a test of loyalty. As Frank approaches, he hefts Mendoza's pistol, points it at Al's head and pulls the trigger. The pistol dry-fires and a thug slips a plastic bag over Al's head. Frank asks for his pistol back, IDs himself as an agent and shoots both of Mendoza's thugs. Mendoza tries to shoot Frank, but his weapon jams, and he is quickly captured. Frank later admits to Al that the pistol could have had at least one round in the chamber.
A few days later, Frank investigates a complaint from an elderly landlady who says that one of her tenants, Joseph McCrawley, has been acting mysteriously. When he enters the man's apartment, he finds paraphernalia related to several presidential assassinations, especially John F. Kennedy's. Frank was an agent assigned to Kennedy when he was assassinated in Dallas in 1963, and still feels remorseful that he didn't prevent it. A further search of the room reveals that McCrawley is a skilled machinist who builds model racing cars. What Frank doesn't see is that McCrawley, whose real name is Mitch Leary (John Malkovich
), is watching him through binoculars from across the street.
They quickly determine that the guy is using a phony name as the real Joseph McCrawley died many years ago. Al and Frank return to the apartment later to find that it's been emptied and that the shrine to the dead presidents has also vanished. A single picture remains, one of a much younger Frank serving on Kennedy's detail. Frank's face has been circled in red.
Frank goes home that night, and receives a phone call from Leary. He tells Frank to call him "Booth" after Lincoln's asassin because the man had more "flair and panache". Leary tells Frank he plans to assassinate the current president (Jim Curley
) and hopes that Frank will be assigned to the case. Leary seems to have a deep admiration for Frank. While on the phone, Frank hears a fire engine passing by Leary's location. Suddenly, he hears the same fire engine rush past his apartment and through the phone line. He runs to the pay phone on corner near his building, and finds the phone hanging off the hook, Leary having already vanished.
Frank meets with the Secret Service's director, Sam Campagna (John Mahoney
), and tells them he thinks Booth is definitely dangerous. He agrees to have himself and Al continue their investigation and also asks for his phone to be tapped. Frank has an adversarial relationship with a younger assistant director, Bill Watts (Gary Cole
), who thinks Frank is a burnout. At the meeting, Frank also meets a female agent, Lilly Raines (Rene Russo
), whom seems charmed by Frank but also sees through his tough-guy exterior. Later, Frank shares a drink with Sam and requests to be added to the current president's protection detail. Sam suggests he may be too old for the detail but agrees.
Leary calls Frank again, still using the "Booth" name, telling him that he was watching him that day while Frank was running alongside Kennedy's limo and working crowd control. He also talks in great detail about Frank's history after the Kennedy assassination. Frank had become an alcoholic and his marriage had broken up. Frank checks with the men tapping his phone line and they tell him they've got a location on Leary. However, when the police raid the house, they find Leary has used a signal jammer to trace the call to a civilian home.
Frank later takes Lilly out for ice cream at the Lincoln Memorial. Though Frank is charming, he still tells Lilly that he believes that female agents work in the Service simply because the President wishes to court the female vote throughout the country. Moments later he determines she may be infatuated with him because of a small gesture as she walks away.
Meanwhile, Leary changes his facial hair and flies to Los Angeles. Using the alias name James Carney, he goes to a downtown bank to open up a new bank account in the name of a fictitious software corporation. While he talks to the account specialist, Pam Magnus, he offhandedly mentions that he's from Minneapolis, which just happens to be the same city that she's from. Though he's pleasant with her, Leary suspects she may interfere with his plans and he may have left enough of an impression on her that she'll remember him. So he follows her home and bluffs her into letting him into her house, and then kills her and her housemate by breaking their necks.
Leary returns to Washington and engages Frank in another phone call. Frank becomes infuriated when Leary suggests that Kennedy had a suspicion he'd be assassinated and that he had a death wish. Leary also claims that Kennedy didn't care about the ramifications of his own assassination when he refused to have agents traveling closer to his motorcade in Dallas. The two men tracing the call trace Leary to a phone booth in Lafayette Square, just across the street from the Executive Office building. Everyone runs outside to the park, searching the area for their target. Frank spots a hippyish-looking man with long hair and instinctively knows it's "Booth". He runs after him, quickly becoming winded. Leary causes a minor fenderbender and is hit by another car; when he lands on the hood, he touches the windshield. Frank immediately orders the car impounded so they can lift fingerprints.
When the FBI matches the prints, they discover that they belong to a former government agent. The information is not shared with either Frank or Al. Frank charges Al with continuing the investigation while he works on protection in the Midwest and Western United States. At one stop Frank works outside in heavy rain and cold temperatures and comes down with a minor illness. Leary is present at an indoor rally in Chicago. He uses a pin to burst several balloons that the ill Frank mistakes for gunshots. He yells for the detail to escort the President from the room, causing a minor panic. The President resumes his address. Frank is subsequently reprimanded by White House Chief of Staff Harry Sargent (Fred Dalton Thompson
), who seems more concerned with the upcoming election than providing adequate security for the president.
Frank returns to his DC home to recover from his illness. Al shows up and tells Frank that he'd made a connection between "Booth" and his model car hobby. Frank and Al go to Pasadena, Caifornia to check on the lead; they talk to a professor of design engineering who mentions that a year ago, he met a fellow model car designer who seemed friendly, but seemingly turned angry when the conversation turned to politics. He suggests that they talk to a man in Phoenix named Walter Wickland. Wickland, upon being shown the sketch, identifies Leary, who he hasn't seen in a year. Wickland reveals that Leary beat him up severely for allegedly ripping off one of his designs, enough that he is paralyzed and confined to a wheelchair, and he now carries a pistol around that he intends to use to kill Leary if Leary ever returns.
Frank and Al drive to Leary's address and break into the house, inadvertently crossing paths with CIA agent David Coppinger (Steve Railsback
) and another agent who are pursuing Leary because of the fingerprints Frank turned up. A background check shows that Leary was a former CIA contractor, trained to be a wetwork specialist, but negative psychological screenings, combined with budget cuts, resulted in his dismissal from the agency. He didn't take it too well and never was able to adjust to civilian life. For instance, when a friend of his stopped by his Phoenix place to convince him to get counseling, Leary responded by slitting his throat.
Leary, meanwhile, goes out to a pond to test out a homemade gun made of a plastic material. While he shoots it, a couple of hunters find him. He lets them try out his pistol; when one of them offers to buy it, he tells them he needs it to assassinate the President, at which point he promptly kills both men and leaves.
Al drives Frank home one night and seems distraught. He tells Frank that he has recurring nightmares of the incident on the boat and of the plastic bag being placed over his head. He thinks that transferring off Frank's detail will be a better option. Frank tells Al to toughen up and that he needs him to help with the investigation. Al agrees.
When Leary calls again Frank confronts him, telling he knows his name and that he's closing in. Frank also taunts Leary with the knowledge of Leary having killed his own friend. Leary insists that the CIA did not simply fire him, they sent his friend to eliminate him. They turned him into a psychotic killer, and now they want him dead because they "can't have monsters roaming the countryside."
The tracing experts finally track Leary to an apartment in Northeast DC. The authorities move in as Al and Frank arrive, but Leary has already left in advance of the raid. Frank and Al spot Leary and chase him along several rooftops; in the process, Al falls behind Frank. Leary jumps a considerable distance from one building to another; when Frank follows, he misses the ledge and hangs off above an alley. Leary appears above him and tells Frank to take his hand or fall. While Frank holds on he draws his pistol and points it at Leary. Leary taunts Frank, telling him that he can shoot him and save the president, thereby falling to his death, or let Leary rescue him. Al arrives, wanting to shoot.
Frank continues to point his pistol, seemingly resolved to shoot Leary; Leary deliberately bites down on the muzzle of Frank's pistol, then throws him to safety on a fire escape. Al yells for Leary to freeze and holds him for a few seconds, however, he becomes distracted and Leary fatally shoots Al. A search of Leary's apartment turns up a scrap of paper with the word "S.W. KELLUM LA" on it. It proves to be something of a dead end, with no person of that name in Los Angeles or Louisiana. Later, Frank rides the bus home, looking very distraught. He's at a bar when he gets another call from Leary, who again taunts Frank, saying he killed Al in self-defense. Frank ends the conversation, saying he'll desecrate Leary's grave after he catches and kills him.
As Leary proceeds to alter his appearance again, Sam attempts to convince Sargent to cancel the President's upcoming visit to Los Angeles. Sargent refuses, as the President cannot afford to lose California's votes, but grudgingly agrees to upgrade security. However, while they are making preparations for the dinner party at the Westin Bonaventure Hotel, Frank mistakes an innocent bellboy for a security threat and roughs him up in full view of reporters. Sargent considers this the last straw, and Lilly is forced to remove Frank from the detail. Leary, resuming his alias as James Carney, meets the gentleman in charge of the dinner ceremony, Sanford Riggs (w/ whom he'd spoken previously), who gives him tickets to the dinner. Riggs & Leary/Carney are chatting in the hotel, when Frank calls Riggs over to ID some photos, Leary is unfazed.
Lilly talks with Frank about his obsession with Leary and tells him he's not alone and should rely on his fellow agents more. He talks about his failure to protect JFK and how it made him feel. Lily takes his hand and they stand at a window looking out at the LA skyline.
Frank talks to another agent who tells him a number to call and that he remembers it as "ukelele." When Frank goes to dial that number, he realizes it's awfully similar to S.W. Kellum. He dials the number and gets South West Savings and Loan, the bank where Leary set up his Carney ID. When he visits the bank, he's told about the murder of the account specialist. The other bank employees try to ascertain new accounts she was working on just prior to her murder and Frank asks them to fax him the list of names. Meanwhile, Leary/Carney enters the dining hall.
The President arrives while Leary assembles his composite plastic gun under the table, making small talk with the woman seated next to him. Frank is rushing to the hotel in a cab. When he arrives, there's a fax waiting for him with the new accounts from the bank; he matches the names against the list of contributors and finds James Carney. While Watts accosts him, he gets a seating chart and finds Leary, then rushes toward him just as Leary raises his pistol to shoot the president, arriving just in time to take the bullet.
Chaos ensues as the President is spirited away, and Leary switches to a regular gun and takes Frank hostage, dragging him into a glass elevator. Frank is revealed to be wearing a bulletproof vest, and he discovers that the microphone in his collar is still connected to Lilly's frequency. Leary points his gun at Frank, saying that he will not be taken alive, but he's taking Frank with him. Frank tells him to pull the trigger and get it over with, and Lilly correctly deduces that this is an instruction to her. Leary, thinking that Frank is talking to him, demands that Frank acknowledge that he gave him the new sense of purpose he has now. When Frank says to "aim high," Leary finally catches on, and ducks just as the snipers blow out the elevator windows. Frank and Leary fight, and snipers are not able to get a solid bead on either of them. Leary eventually loses his footing and ends up hanging off the railing, with Frank offering him a hand. Leary refuses, and lets himself drop a few dozen stories to his death.
Frank, now hailed as a hero, announces his retirement from the Secret Service at the airport; he is too old to be running alongside limousines, and he cannot do undercover work now that his picture has been circulated on every newspaper in the country.
Lilly and Frank return to Frank's apartment in D.C. to find a message on his answering machine from Leary. They ignore the message, opting for a quiet moment at the Lincoln Memorial's reflecting pool.