In a tense opening set inside a phone box in Spain, the impersonator Adam O'Brian Adam O'Brian calls the police claiming to be a tourist who has found a young boy and requests that the boy be collected. He is taken to a children's home and insists he is American. He asks to be left alone in an office overnight so he can contact his family, and there, he begins to work a meticulous ruse. He combs through records to reach various sheriff's offices in the United States, probing for information about missing children. From one lead he lands the name Nicholas Barclay, and then he calls another U.S. agency, posing as a Spanish official and asking for a faxed file on Nicholas. This marks the start of an elaborate attempt to pass as Nicholas, even plotting with tattoos and hair dyed blond to better resemble the missing boy.
Nicholas's family is notified of the discovery, and his sister flies to Spain to bring him home. A court accepts the identification, and he is declared a U.S. citizen. She transports him back to San Antonio, Texas, where most of the family accepts him, with the mother especially eager to welcome him and affirm him as her son. The young man at the center of this case appears to have found a place among relatives who want to believe him, even as doubt simmers beneath the surface.
But Bourdin turns out to be a man with a long history of impersonating children, real or imaginary, and he deepens his deception by alleging a brutal backstory—kidnapping for sexual abuse by Mexican, European, and U.S. military personnel and transportation from the United States to Spain. His impersonation fools a number of officials in both Spain and the United States, and many Barclay family members seem willing to accept him despite clear mismatches—he is seven years older than Nicholas, speaks with a French accent, and has brown eyes and dark hair instead of Nicholas's blue eyes and blond hair. The illusion begins to crack only when a private investigator, Charles Parker, and an FBI agent, Nancy Fisher, push back against the narrative and pursue the truth.
Bourdin is eventually arrested, and Interpol confirms his identity and long criminal record. In custody, he tells the police that the family killed the real Nicholas and that his presence was a cover for that crime. The remaining family scapegoats—most notably his dead brother Jason—are dragged into the mounting suspicion, challenging the fragile web of belief that had formed around the impostor.
Layton offered a pointed reflection on Bourdin's influence and charm: "He invites sympathy. He has this childlike quality about him, and he can be very charming. And at other times he can be quite repellent, because he can be remorseless and you're reminded about what he did. So as a filmmaker, I was asking: how can I find a way of getting the audience to experience a bit of that?"
