North by Northwest, one of Alfred Hitchcock’s most popular films, is an epic story of government intrigue and mistaken identity. The story begins with Roger Thornhill, a successful advertising agent in New York, dictating a letter to his secretary as they walk through his office building. Roger proceeds to The Plaza Hotel, where he has a business meeting. Once there he signals a pageboy, who is asking after "George Kaplan," and is mistaken for George Kaplan by two thugs standing nearby. Roger is immediately abducted by the two men who believe him to be Kaplan. They take him to a remote mansion on Long Island where he is questioned by a soft-spoken man claiming to be named Townsend. Despite Roger’s denial and confusion, the man who calls himself Townsend is convinced that Roger is Kaplan and has his henchmen forcibly intoxicate him. Completely drunk, Roger is driven to the edge of a cliff by the men who try to stage a false suicide, but he manages to escape, taking control of the vehicle and eventually being taken in by the police, who arrest him for drunk driving.
When no one believes Roger's story, he embarks on a mission to discover the truth about George Kaplan, the man for whom he's been mistaken. He arrives at Kaplan’s hotel room at The Plaza, but finds his room deserted. Two of the henchmen corner him in the hotel, but he manages to escape again, making his way to the United Nations, where Townsend supposedly works. Once there, he learns that the man he met at the mansion was not Townsend at all, but an imposter. The real Townsend is an employee of the United Nations, and the criminals are illicitly using his mansion as a base. When Roger shows Townsend a picture of the counterfeit Townsend, one of the thugs—a man named Valerian—throws a knife into Townsend’s back. Roger pulls the knife from his back in the lobby of the United Nations, and instantly finds himself framed for murder.
Roger journeys to Chicago where he thinks Kaplan is staying, and aboard the train meets Eve Kendall, a beautiful industrial designer who befriends him and agrees to keep his secret. Roger and Eve soon fall in love with each other, but it is quickly revealed to the viewer that Eve actually works for the criminal organization that initially abducted Roger. Meanwhile, a meeting at an intelligence agency in Washington D.C. takes place, and we are introduced to the character of the Professor, an elderly man who is the head of the committee. In the course of the meeting, we learn that George Kaplan does not really exist: he is a decoy invented by the intelligence agency to distract the fake Townsend's criminal organization from discovering an actual double agent—employed by the intelligence agency—in its ranks.
Having received a false message from “Kaplan” through Eve, Roger journeys to a deserted farm town where he is nearly killed by an assassin in a stolen crop-duster airplane. Roger manages to escape as the crop-duster flies into an oil truck and explodes. Returning to the city, Roger confronts Eve, whom he now knows is not to be trusted. Roger follows Eve to an auction, where he learns of Eve’s involvement with the false Townsend, whose name is really Vandamm. When Vandamm assures Roger that he will not leave the auction house alive, Roger creates a disruption so that the police will take him away. After being arrested, Roger is taken to the Professor, who convinces him to continue the deception that he is George Kaplan, so that they can maintain the safety of the government agent, who is revealed to be Eve Kendall.
Roger and the Professor follow Vandamm to North Dakota where Eve pretends to shoot Roger in the cafeteria of the visitor center at Mount Rushmore, in order to reassure Vandamm of her loyalty to him. After he is quietly taken to the hospital, having been shot with blanks, Roger learns that Eve is leaving with Vandamm for Europe that evening. After the Professor forbids him to become involved, Roger escapes from the hospital and makes his way to Vandamm’s house near the top of Mount Rushmore. Outside the house, he overhears one of Vandamm’s henchmen, Leonard, inform Vandamm of Eve’s disloyalty, having discovered her blank-filled gun. Having learned this disturbing news, Vandamm plans to kill Eve as soon as they board the plane. Roger manages to warn Eve in time, and the two flee with a statue that Vandamm purchased at the auction, which Roger has learned is full of microfilm. Pursued by Vandamm and his men, Roger and Eve attempt to climb down Mount Rushmore. Just as Vandamm’s men are about to kill them, the Professor arrives with the police. Vandamm is arrested, and Roger and Eve leave on a train together.