Coming across 400 home movies by anyone from the 1930s and forties would have been a social history treasure trove in itself. So it's all the more remarkable to discover those of Harry Birrell, whose cine-camera hobby expands from the standard family holiday larks into a vast, subjective record of the second World War on three continents.
What makes it more special still is that Harry was also, during the war years at least, an assiduous diarist. Hey presto, first person narration to accompany the images, given stalwart voice for the film by Richard Madden (who comes from Elderslie, a stone's throw from Harry's Paisley).
The effect is astonishing, taking us from the courtship rituals of thirties Scotland - beach romance on the Isle of Arran, cinema dates in a sooty Glasgow - through the six years of the war, mostly spent in the subcontinent with the Ghurkas, ever smiling into camera.
Occasionally, we also get the intrusion of newsreel footage to round out the big picture, but it's Harry's - mostly colour - footage that is the star. It simultaneously builds a portrait of a war and of a person increasingly defined by it, through his growing bond with the men, his fears, his longings and eye-popping shots, such as an animal sacrifice, in which the beheading of a bull has been decorously blurred for our benefit.
Perhaps what's most affecting is the growing impression that Harry is changed, both for better and worse, by his time in the war. The diaries stop in 1945, and when we find out that he married in the fifties, the information is tinged with a sadness for the other girl he fell in love with on the Arran beach. There's a profound sense of the passage of time, and the people who flow through a life.
If there's a flaw, it's only in an opportunity missed to provide a framing device that would have made even more of this Aladdin's cave. As it is, we get perfunctory breakaways to Harry's family 'finding' (not really) and tearfully responding to Harry's legacy. It's all fine, but you can't help feeling that these extraordinary films deserved a grander presentation.