I’m accustomed to readers flipping out on me because they think I’ve spoiled a movie for them. (For the record, I try to warn people if I’m going to reveal any big surprise—as I will here—and if they want to stop reading that’s fine with me.) What really blows my mind is readers who complain that I’ve ruined a documentary for them. Such was the case when I reviewed Dear Zachary (2008), about an ugly child-custody battle that ended in August 2003 when the mother killed the child and herself. The story had been national news, but somehow I was to blame for mentioning this shocking development in my review, as if I were obliged to protect the ignorant. This puts me in a real jam, because in November I’m going to have to write about Steven Spielberg’s biopic Lincoln and I don’t want to be a killjoy by telling you how the Civil War turned out.

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Grann begins his story in France with a tale of a damaged soul who became a master con man. Frederic Bourdin was born in 1974 to an 18-year-old French mother and an Algerian immigrant whom she never told about the birth. She couldn’t care for the child and left him with her parents; by his teens the boy had become an outcast because of his mixed racial heritage, and by age 16 he’d begun to invent identities for himself as he bounced around Europe from one foster home or orphanage to the next. When he reached adulthood, he kept passing himself off as a minor, partly to take advantage of social services but also to find some sort of guardian or emotional center to his life. Bourdin’s life took a fateful turn in October 1997 when, faced with the threat of prison in Linares, Spain, he contacted the National Center for Missing & Exploited Children in Alexandria, Virginia, and managed to obtain a faxed report on Nicholas Barclay, who had been missing from San Antonio, Texas, since 1994.

Because the boy’s disappearance never got a screaming media treatment, Layton doesn’t have much footage to work with. There are a few photos and video snippets of 13-year-old Nicholas, but most of the story unfolds through talking-head interviews that continue on the soundtrack as actors play out the events being described. Layton is an old hand at this sort of thing, and I can’t fault his storytelling skills as he re-creates the cross-Atlantic drama of October 1997. Carey Gibson became the family’s envoy, flying out to Spain to collect her long-lost brother even as Frederic Bourdin, obtaining a better photo of Nicholas Barclay, discovered to his horror that the boy had blond hair and blue eyes. Layton edits their stories together as they converge, adding a nervous Bernard Herrmann-like score to shots of the 31-year-old woman venturing into a strange land (the actress is a ringer) and the 23-year-old imposter dyeing his black hair and getting cheap tattoos to match the ones reported on Nicholas.

“Show me one piece of evidence . . . just one shred of actual proof,” Gibson demands. “The biggest, funniest one to me—hilarious—is that we went and picked up a complete stranger to hide the fact that we killed Nicholas, or someone in my family killed Nicholas, when, through four years that Nicholas was disappeared, we were the only ones looking for him. Why would we go pick up a stranger to hide something that didn’t need to be hid?” She has a point, but that doesn’t stop Layton from following Charlie Parker out to Beverly and Jason’s old house, whose current owner allows him to dig up the backyard in search of a body, and ending The Imposter with an overhead shot of the two men staring over a deep, empty hole that feels very much like a grave. All they really have is circumstantial evidence and their own suspicions, but those sure make for a juicy mystery. As Gibson herself put it, your heart takes over and you want to believe.

Directed by Bart Layton