冒充者 The Imposter (2012)

This documentary begins in mystery and ends in horror – a disturbing vision of the lengths we go to, to fool ourselves.

Bizarre true-life stories, in documentary or feature form, have long been a staple of the Sundance film festival – increasingly so since the breakout debut of Andrew Jarecki's startling Capturing the Friedmans in 2003. This year, the shock ticket looked to be Craig Zobel's dramatized piece Compliance, in which the staff of a small-town fast-food joint are pranked into astoundingly serious sexual misconduct. But while it never strays into such lurid territory, Bart Layton's documentary The Impostereclipses it with a story that is really two in one: starting as a macabre Patricia High smith-like Ripley story and ending as a full-blown American gothic horror.

It begins in 1994, when 13-year-old Nicholas Barclay goes missing from his home in San Antonio, Texas. Three years later, a boy answering to a similar, but by no means identical, description turns up in Linares, Spain. Without really conducting any in-depth inquiries, his sister arrives to whisk him home, where even his mother doesn't seem to notice that her once fair-haired son is now a bottle-blond with a five o'clock shadow, speaking with a pronounced French accent.

Layton doesn't waste much time on the mystery, revealing in the film's set-up that the boy is not a boy at all but a 23-year-old drifter with a penchant for being taken in by care homes. But what Layton keeps carefully at bay for the film's trim 95-minute running time is the stranger's identity. Talking to camera, he talks us through his ruse with a sociopathic good humour, and the callousness of his thinking is matched for sheer horror only by the ineptitude of the authorities who allowed him to get away with it. In these scenes, the film resembles Man on Wire, with the stranger letting us in on his plan, just as, in that film, Philippe Petit invited us to marvel at his assault on the World Trade Centre.

This story in itself would be enough, but, like any good modern documentary, The Imposter has more twists and turns to reveal. These come courtesy of American private eye Charlie Parker, who was asked to investigate the story by a national news channel. But what Parker found out didn't just blow the lid on the real identity of the interloper, it shed a disturbing new light on the Barclays, suggesting a hideous game of double-cross in which the new "Nicholas" was actually a pawn rather than a player. Despite eyewitness accounts from almost all concerned, The Imposter never actually resolves this tantalising new storyline, and its ambiguous ending borders on unsatisfactory, given the depth of the research undertaken.