My Old School, review: the riveting, unnerving tale of the 30-year-old who pretended to be a teenager

Ordinarily, a documentary whose subject refused to appear on camera would be at a serious disadvantage. In the case of My Old School, that refusal is the making of it.

This impish and riveting talking-heads piece recounts the stranger-than-fiction case of the Scottish hoaxer known as Brandon Lee, who in 1993 joined the fifth year at Bearsden Academy in Glasgow under what could be called ambitiously false pretences. The curly-haired, Canadian-accented teen was in fact a 30-year-old local man called Brian McKinnon whose longstanding ambition to train as a doctor had come to naught: this deception, he believed, would let him take a second swing at medical school, the cut-off age for which he had now passed.

When Lee’s scheme came to light in 1995 he became a minor media sensation, even appearing on breakfast television to coyly discuss his tactics and motives. He’s less keen to plead his case in person these days, however, so director Jono McLeod has devised a cunning compromise: an audio confession from Lee which is then “performed” by the actor Alan Cumming, who silently lip-synchs along to Lee’s words. The result is less a piece of acting than human-on-human ventriloquism, and keeps the viewer fizzing with suspicion throughout.

Alongside Lee’s own creepily compelling testimony are interviews with his ex-classmates and animated recreations of pivotal moments, which owe a visual debt to the opening titles of Grange Hill (this being Scotland, the fork-skewered banger flying across the cafeteria has been wittily replaced with a square of Lorne sausage). The voice cast for these segments features two talismanic presences: Clare Grogan, who played Susan in Gregory’s Girl, and Lulu, who also provides a perky theme song for the closing credits.

For about an hour, McLeod’s film bubbles along entertainingly, savouring the wildness of the tale while occasionally labouring its ironies, which most viewers will spot first time around. But then something exciting and unnerving happens: the “true story” Lee’s classmates have been telling for the past 25 years is also gradually revealed to be a semi-fiction, whose more awkward and troubling corners have been subconsciously sanded off. A video recording of a school play proves one collective memory decisively false – and the ex-pupils’ reactions on being confronted with the truth is the kind of documentary moment that tingles for months.

15 cert, 104 min. In cinemas from Friday August 19