This is the story of a documentary film – perhaps the best documentary ever made – and the treacherous truth that lurked behind the celluloid. It is a gripping tale, a kind of minor epic infused with the plangent loneliness of the polar regions, and Melanie McGrath tells it with panache.

The film was Nanook of the North, the director a dogged Irish-American called Robert Flaherty who pitched up, in 1920, among a group of Inuit on the Ungava Peninsula, in Inukjuak on the east coast of Hudson Bay. He had been trying to make a film in the Arctic for years. This time he used Akeley cameras fitted with gyroscopic tripod heads and lubricated with graphite rather than oil (which froze). For a year, living in the abandoned cabin of a fur-trader, Flaherty filmed the daily life of his neighbours. Difficulties queued up – insufficient daylight, dry snow in the lenses, film which shattered in the cold (that was only the start of it), but Flaherty sailed home to New York with 75,000 feet of film. The edited version was and remains a triumph. Who can forget the image of the hunter Nanook steadying his kayak while, from the impossibly tiny hole at the stern, one wife emerges, then another wife, then a series of children of ever decreasing size, and, finally, the dog? 

Nanook’s story captured the imagination of the world. ‘To this audience,’ writes McGrath, ‘still reeling from the trenches and the mustard gas of the First World War, Nanook and Nyla [one of his wives] were innocent wanderers in an as-yet unblemished world.’ A still of the plucky little hunter was