In 1972, Mason Skiles (Jon Hamm) is a U.S. diplomat in Lebanon and lives in Beirut with his Lebanese wife, Nadia (Leila Bekhti), and has recently begun caring for Karim (Idir Chender), a 13-year-old Palestinian boy who claims he is without a family. While hosting a party, Skiles is confronted by his friend, CIA officer Cal Riley (Mark Pellegrino), who wishes to question Karim, whose brother has been linked to the 1972 Munich massacre. The party is attacked by Karim's brother, Rami (Ben Affan), who abducts Karim; in the ensuing gunfight, Nadia is killed.Ten years later, Skiles has become an alcoholic and is working as a self-employed labor arbitrator in New England. While arbitrating a labor issue between particularly intransigent parties and struggling to keep his small firm afloat, he is approached by Sully (Douglas Hodge), an old client, on behalf of the U.S. government. Sully tells Skiles that he has been requested for an academic lecture in Lebanon, and hands him money, a plane ticket, and a passport. Skiles is initially resistant but decides to travel to Beirut. He meets several State Department officials, Donald Gaines (Dean Norris), Gary Ruzak (Shea Whigham), and Frank Shalen (Larry Pine), along with CIA officer Sandy Crowder (Rosamund Pike) (a CIA field agent working undercover at the American embassy) and learns that Cal Riley was recently abducted in Lebanon, and his kidnappers requested Skiles to negotiate his release.The group meets with the kidnappers, where they learn that Karim is leading the organization. Karim demands the release of his brother in exchange for Riley, despite the Americans' protest that they do not have Rami in captivity. Skiles suspects that Israel is holding Rami, and travels with Ruzak to secure his release for the exchange. The Israelis reveal that they do not have Rami, and Skiles returns to Beirut to meet with Alice (Kate Fleetwood), Riley's wife. Alice holds Skiles responsible for Riley's abduction, as she believes that he has remained in Lebanon over the guilt he feels for Nadia's death. Roni Niv (Alon Abutbul) meets Gary in secret and confirms that Israel doesn't have Rami in captivity. He wants Gary to publish the news of Cal's death and allow Israel to invade Lebanon to clear the place out of the PLO and other Islamist factions. Gary is skeptical of Israel & Mossad's motives and doesn't want to give up on Cal too easily.The next day, Skiles is giving the lecture that was his official reason to travel to Beirut when a car bomb is set off outside the building. In the ensuing chaos, Skiles is instructed to leave to meet Karim. Karim brings him to Riley, who covertly tells Skiles that the Palestine Liberation Organization (PLO) is holding Rami, and that Gaines is not to be trusted. Before releasing Skiles, Karim gives him an ultimatum for later the same night to return Rami, or he will sell Riley to Iran. Skiles returns to Riley's apartment to search for clues, where he encounters Crowder. She reveals that Gaines had been stealing money from the embassy, and that Riley had been preparing to make a report shortly before his disappearance. Skiles now understands that Gaines knew about Cal's knowledge of his theft and hence has every reason that Cal is never released and dies in custody of Karim. Meanwhile Gary wants Israel to attack Lebanon so that Beirut can be cleaned off in one go. So he wants Cal to die in custody and that gives US every reason to step out of Israel's way to invade Lebanon. Skiles convinces Crowder that the PLO is holding Rami, and she steals $4 million from the CIA office to trade for Rami.After Skiles attacks a senior PLO officer in his own home, he sets up a trade for Rami and brings him to the exchange with Karim. After trading Riley for Rami, but then Rami decides to attack Skiles, and then Rami is shot and killed by a hidden Mossad sniper in a nearby building; the Americans successfully escape. Before departing Beirut, he learns that Gaines has unexpectedly retired, and Ruzak has left Beirut. Crowder announces her intention to apply for the newly vacant jobs, and Skiles offers his services as a negotiator.