During his farewell address in 1961, outgoing President Dwight D. Eisenhower warns about the build-up of the military-industrial complex. He is succeeded by John F. Kennedy as president, whose time in office is marked by the Bay of Pigs Invasion and the Cuban Missile Crisis until his assassination in Dealey Plaza, Dallas, Texas, on November 22, 1963. Ex-Marine and suspected Soviet defector Lee Harvey Oswald is arrested for the murder of police officer J. D. Tippit and arraigned with both murders but is killed by nightclub owner Jack Ruby. New Orleans District Attorney Jim Garrison and his team investigate potential New Orleans links to the JFK assassination, including private pilot and activist David Ferrie, but their investigation is publicly rebuked by the federal government and Garrison closes the investigation. The investigation is reopened in 1966 after Garrison reads the Warren Report and notices what he believes to be multiple inaccuracies, such as the single bullet theory. Garrison and his staff interrogate people involved with Oswald and Ferrie, learning that the two were involved with the CIA in Operation Mongoose. One witness, Willie O'Keefe, a male prostitute serving five years in prison for solicitation, says that he witnessed Ferrie talking with a man called " Clay Bertrand " about assassinating Kennedy, and that he briefly met Oswald. Garrison and his team theorize Oswald never actually "defected" and was in fact an agent of the CIA who was betrayed and framed for the assassination. In 1967, Garrison and his team talk to several witnesses, including Jean Hill, a teacher who says she witnessed a gunman shooting from the "grassy knoll", a small hill, that Secret Service threatened her into saying three shots came from the Texas School Book Depository from which Oswald was said to have shot Kennedy, and her testimony was altered by the Warren Commission. Garrison's staff also test fire an empty Carcano rifle from the Depository and conclude that Oswald was too poor a marksman to make the shots, and that there was more than one shooter. Garrison comes to believe that "Bertrand" is really New Orleans businessman Clay Shaw. Garrison interviews Shaw, who denies having ever met Ferrie, O'Keefe or Oswald. Some key witnesses become scared and refuse to testify while others, such as Ruby and Ferrie, die in suspicious circumstances. Before his death, Ferrie tells Garrison that there was a conspiracy to kill Kennedy. Garrison meets a high-level figure in Washington D.C. who identifies himself as "X", who claims Kennedy's security in Dallas was deliberately neglected. He also suggests a coup d'état at the highest levels of government, implicating members of the CIA, the Mafia, the military-industrial complex, Secret Service, anti-Castro Cubans, the FBI, and then-Vice President Lyndon B. Johnson as either co-conspirators or as having motives to cover up the truth of the assassination. X suggests that Kennedy was killed because he wanted to pull the United States out of the Vietnam War, halt further actions against Cuba, and dismantle the CIA. X encourages Garrison to keep digging and prosecute Shaw. Soon afterward, Garrison indicts Shaw with conspiring to murder Kennedy. Garrison's marriage is strained when his wife Liz complains that he is spending more time on the case than with his own family. After a sinister phone call is made to their daughter, Liz accuses Garrison of being selfish and attacking Shaw only because of his homosexuality. Some of Garrison's staff begin to doubt his motives and disagree with his methods, and leave the investigation. One of them, Bill Broussard, is later revealed to have been an insider for the FBI for some time, and even plays a peripheral, undisclosed role in what seems to be an attempt to kidnap, murder or otherwise scare Garrison. In addition, Garrison is criticized in the media as wasting taxpayer money to investigate a conspiracy theory. Garrison suspects a connection with the assassination of Martin Luther King Jr. and the assassination of Robert F. Kennedy. Shaw's trial takes place in 1969. Garrison presents the court with a dismissal of the single-bullet theory, proposing a scenario involving three assassins firing six shots and framing Oswald for the murders of Kennedy and Tippit, all for the purpose of installing Johnson as president so he could escalate the war in Vietnam and enrich the defense industry. However, the jury acquits Shaw after less than one hour of deliberation. While his prosecution has failed, Garrison wins his wife and children's respect for his determination, and so repairs his relationship with his family.

On June 17, 1972, Frank Wills, a security guard at the Watergate complex finds a door's bolt taped over to prevent it from locking. He calls the police, who find and arrest five burglars in the Democratic National Committee headquarters within the complex. The next morning, The Washington Post assigns new reporter Bob Woodward to the local courthouse to cover the story, which is considered of minor importance. Woodward learns that the five men — James W. McCord Jr. and four Cuban-Americans from Miami—possessed electronic bugging equipment, and are represented by a high-priced "country club" attorney. At the arraignment, McCord identifies himself in court as having recently left the Central Intelligence Agency (CIA), and the others are also revealed to have CIA ties. Woodward connects the burglars to E. Howard Hunt, an employee of President Richard Nixon 's White House Counsel Charles Colson, and formerly of the CIA. Carl Bernstein, another Post reporter, is assigned to cover the Watergate story with Woodward. The two young men are reluctant partners but work well together. Executive editor Benjamin Bradlee believes that their work lacks reliable sources and is not worthy of the Post' s front page, but he encourages further investigation. Woodward contacts a senior government official, an anonymous source he has used before and refers to as " Deep Throat ". Communicating secretly, using a flag placed in a balcony flowerpot to signal meetings, they meet at night in an underground parking garage. Deep Throat speaks vaguely and with metaphors, avoiding substantial facts about the Watergate break-in, but promises to keep Woodward on the right path to the truth, advising Woodward to " follow the money ". Woodward and Bernstein connect the five burglars to corrupt activities involving campaign contributions to Nixon's Committee to Re-elect the President (CRP or CREEP). This includes a check for $25,000 paid by Kenneth H. Dahlberg, who Miami authorities identified when investigating the Miami-based burglars. However, Bradlee and others at the Post still doubt the investigation and its dependence on sources such as Deep Throat, wondering why the Nixon administration should break the law when the president is almost certain to defeat his opponent, Democratic nominee George McGovern. Through former CREEP treasurer Hugh W. Sloan Jr., Woodward and Bernstein connect a slush fund of hundreds of thousands of dollars to White House chief of staff H. R. Haldeman —"the second most important man in this country"—and to former attorney general John N. Mitchell, now head of CREEP. They learn that CREEP was financing a " ratfucking " campaign to sabotage Democratic presidential candidates a year before the Watergate burglary, when Nixon was lagging Edmund Muskie in the polls. While Bradlee's demand for thoroughness compels the reporters to obtain other sources to confirm the Haldeman connection, the White House issues a non-denial denial of the Post' s above-the-fold story. Bradlee continues to encourage investigation. Woodward again meets secretly with Deep Throat and demands that he be less evasive. Very reluctantly, Deep Throat reveals that Haldeman masterminded the Watergate break-in and cover-up. He also states the cover-up was not only intended to camouflage the CREEP involvement, but also to hide "covert operations" involving "the entire U.S. intelligence community", including the CIA and Federal Bureau of Investigation (FBI). He warns Woodward and Bernstein that their lives, and those of others, are in danger. When the two relay this information to Bradlee and tell him of the depth of the conspiracy, Bradlee realizes that a constitutional crisis is coming, but tells them to move forward with the story. During the second inauguration of Richard Nixon on January 20, 1973, Bernstein and Woodward type the full story, while a television in the newsroom shows Nixon taking the oath of office for his second term as president. A montage of Watergate-related teletype headlines from the following years is shown, ending with the report of Nixon's resignation and the inauguration of Gerald Ford on August 9, 1974.

Following the end of World War II in Europe and the liberation of Denmark from German occupation in May 1945, the Wehrmacht and SS occupiers became prisoners of war. A group of young German prisoners are sent to the west coast where they are trained to use their bare hands to remove the landmines that the Germans had buried in the sand. After their training, the boys are left under the charge of Danish sergeant Carl Leopold Rasmussen, who is determined to treat the young prisoners without sympathy. Marching his squad onto the dunes, he promises that they will return home in three months, if they can each defuse six mines per hour for a total of 45,000 mines. One of the boys, Sebastian Schumann, attempts to remain optimistic as they discuss their plans for when they return home. The POWs are given little food due to post-war shortages and begin to suffer from malnourishment, with Ernst befriending a young local girl to steal some bread from her. One day, while defusing a mine, Wilhelm's arms are blown off and he later dies in a field hospital. Most of the boys become ill after eating grain contaminated with rat faeces that they found on a nearby farm; they are treated by Rasmussen who makes them purge themselves with seawater. Rasmussen gradually treats his charges more kindly, stealing food from the base for them and tries to maintain morale by reporting that Wilhelm has survived. He also allows the boys to use a device invented by Sebastian to improve productivity. Hearing rumours of Rasmussen stealing food for the boys, his commanding officer Captain Ebbe Jensen brings a group of British soldiers to abuse and torment the boys. Rasmussen stops them but is confronted about the theft by Ebbe, who accuses him of being sympathetic towards the Germans. During another day of demining, Werner is blown to bits after encountering landmines buried one above another, leaving his twin brother Ernst distraught. After a casual game of football, Rasmussen's dog is blown up in a supposedly cleared zone of the beach. This causes Rasmussen to snap and begin abusing the boys again. He forces them to march close together across the cleared zones of the beach to confirm that they are safe. When a young local girl walks out into an uncleared area of beach, her mother comes looking for Rasmussen only to find him gone. The boys volunteer to help save the girl. Ernst walks through the uncleared minefield to keep the little girl calm whilst Sebastian clears a path to safety for her. They manage to rescue her but instead of returning to safety with Sebastian, Ernst decides he cannot go on without his brother and commits suicide by walking into the uncleared section and is promptly killed. After witnessing this act of kindness and bravery from the boys, Rasmussen relents in his treatment of them and reassures a grieving Sebastian that they will soon be able to go home. While four of the boys continue to clear the beach with Rasmussen, the rest of them are loading unexploded mines onto a truck. When one of the boys tosses a mine that was not properly defused onto the truckbed of deactivated mines, he accidentally sets off a massive explosion which kills himself and his nearby comrades. Only Sebastian, Ludwig, Helmut and Rodolf remain. Although the boys had been promised that they would be sent home after defusing all of the mines, without Rasmussen's knowledge Jensen decides to send the surviving four to join a team defusing landmines in another coastal area. Rasmussen argues in vain for Jensen to rescind the order. He decides to rescue the boys and then drives them within 500 metres (1,600 ft) of the German border so they can run to their freedom.