A 21-year-old girl's body is found on Hampstead Heath. It turns out she is Sapphire Robbins, a music student, pregnant and planning to marry an architectural student. And it also transpires that she is, to use the parlance of the film, 'coloured' - but she can pass as white, which is what she had done for several months after earlier being part of the black dance and music scene.
Her brother (played by Earl Cameron) is a doctor in Birmingham - and black. He and Sapphire had the same parents - white father and black mother (at least, I think it was that way around) - but a very different appearance.
Many of the streets shots are local - the student architect and his family live at 2 Oakford Road, and his father's sign painting workshop is now where the environmental undertakers keep their corpses. The student's sister works at a dairy - in other words an old fashioned grocer's - on York Rise. There are also street shots of Fortess Road and Dartmouth Park Hill. Really interesting to see the place as it was almost sixty years ago - and looking, if truth be told, distinctly drab. Rationing was over by 1959 but, club scenes apart, this wasn't swinging London.
Just as intriguing are the scenes filmed in west London - if not in Colin MacInnes's Notting Dale (his novel Absolute Beginners appeared in the same year as 'Sapphire') then very much in that mould: the Tulip Club with black musicians and a largely black clientele ... the grim, paint-peeling lodging houses ... the racist Teddy Boy thuggery ... the male Caribbean camaraderie.
It's a police movie, and unsettlingly candid in its depiction of both malign and casual racism. And very interesting in looking at the phenomenon of mixed-race youngsters who decide to pass for white because it helps to sidestep racism and offers them greater opportunities, social and professional.
Earl Cameron spoke powerfully and effectively tonight about the poison of racism - and about his chance entry into acting. He was born in Bermuda, worked as a merchant seaman, and only arrived in the UK when he found himself in Buenos Aires as war was declared in 1939 - while the American members of the crew were repatriated, the Brits (and Earl counted as one because he came from a British colony) were told they had to sail the vessel to London. Once here, for months he couldn't find a job, simply because of the colour of his skin.
Earl Cameron is a CBE, and in a little over a year will celebrate his hundredth birthday - and he still has stage presence. He's a star!
And so are the people behind the Dartmouth Park Film Club - who not only organised the screening, but also brought Earl Cameron and his wife down from their home in the Midlands, organised wine, cake and popcorn ... and were rewarded with a hugely bigger turn-out than the Holloway Odeon usually manages and, I trust, a bumper collection which will help them stage more really good movies and community events.
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