The power of persuasion is far more powerful than we would wish to believe.

Psychic mediums are a case in point. The most successful proponents of this brand of entertainment can attract hundreds, sometimes thousands of paying customers to their shows; people who are ready and willing to be told what they want to believe. Providing information that can often generously be described as ‘vague’, they usually allow their participants to fill in the blanks and do the work for them.

Although not claiming to be able to speak to the spirit world, Frédéric Bourdin is no less accomplished when it comes to manipulation, as the riveting documentary The Imposter reveals.

That being said, a con man will never succeed without willing participants and Bourdin lucked out beyond his wildest dreams when he inveigled himself into the family of Texan teen Nicholas Barclay, who went missing aged 13 in 1994.

It’s a story that staggers belief. More than three years after Nicholas disappeared, the grieving family received a phone call saying he had been found in Spain. Nicholas’ dumbfounded sister Carey immediately flew out to collect him. What no-one knew was that the call to the family had been placed by Bourdin, whose only resemblance to Nicholas was that they each had five fingers and toes.

Nicholas was blonde, blue-eyed and American; Bourdin had dark hair, brown eyes and spoke English with a heavy French accent. He was also seven years older than Nicholas. Although convinced he wasn’t going to get away with it, Bourdin nevertheless dyed his hair, got the same tattoos that Nicholas had and presented himself to Carey … who incredibly took him in as her long-lost younger brother without question.

Remarkably, the con continued to stick upon their return to Texas, as Nicholas’ mother Beverley and other close family accepted him back into the fold. “He had changed so much it was mind-boggling,” said Beverley, who put his dramatic change of appearance down to his traumatic experiences.

Bourdin also fooled the media and FBI agent Nancy Fisher, who had serious suspicions but was convinced (at least initially) by the incredible story he spun about being abducted by an international vice ring. In fact it wasn’t until private invetigator Charlie Parker got involved and unearthed damning evidence of Bourdin’s fraudulent behaviour that the Frenchman realised the game was up.

It’s an astonishing tale and director Bart Layton, until now best known for his nightmare-in-paradise TV series Banged Up Abroad, is wise enough not to pull a Nick Broomfield and just let his subjects do the talking.

Instead he nods to the great documentarian Errol Morris by splicing reenactments with talking heads footage, at times so flawlessly as to underline just how blurred the line between fact and fiction became during this tangled, sorry mess.

It almost goes without saying that Bourdin is perhaps the ultimate unreliable narrator. A man so consumed by his serial addiction to impersonating other people (he claims to have assumed more than 500 false identities) that he was nicknamed ‘The Chameleon’ by the media, Bourdin is nothing if not fascinating. His selfish single-mindedness (“I care about myself, just about myself and f*ck the rest of it” – this coming from a man who’s since got married and had kids) is matched only by his superhuman intransigence.

Although Layton gives the lion’s share of the screen time to Bourdin, he doesn’t neglect Nicholas’ family, specifically Carey and Beverley who are both given ample time to address the question anyone who watches The Imposter will ask – how could they have been so spectacularly wrong?

Bourdin, as well as Parker and Fisher, claim certain members of the family knew a lot more about Nicholas’ disappearance than they were willing to reveal. Layton doesn’t allow the film to take a firm position on this; instead choosing to concentrate more on the humiliating, tragic subterfuge.

Bourdin feels that Carey (and by extension the rest of the family) probably knew deep down that he wasn’t their loved one, but were willing victims regardless, stating: “She (Carey) decided I was going to be her brother.”

Revealingly, the family recount the web of lies spun to them (speaking to the side of the camera – Bourdin is the only one who speaks straight to the camera) as if they are still facts. At no point do they say “he claimed this…”, rather each part of Bourdin’s story is oddly still taken at face value it seems.

Fifteen years on from those extraordinary events there remains bitterness and hurt within the family and a collective sense of bewilderment that will quite possibly never fully disappear. Carey may as well be speaking for the family (and the rest of us) when she asks: “How could I be so f*cking stupid?”

The Imposter often transcends the documentary format, moving into the realm of psychological thriller, especially in the breathless closing 30 minutes when the house of cards that Bourdin has built starts to collapse. It’s a suitably gripping conclusion, handled superbly by Layton, to what will undoubtedly be seen as one of the best documentaries of the year.