When the body of a young, white girl who has been stabbed several times is discovered on Hampstead Heath, the only clue is a handkerchief monogrammed with the initial 'S'. She turns out to be a music student named Sapphire. The police search for her murderer begins with her boyfriend David Harris, a gifted architecture student who has won a scholarship in Rome. Harris claims he was in Cambridge and did not return until late.
The autopsy reveals Sapphire was three months pregnant. When her brother, Doctor Robbins, arrives from Birmingham, he is black – Sapphire had mixed parents.
Investigating Sapphire's story, the police find she lived a double life: both passing for white and visiting black nightclubs. A torn picture found in her boarding room sparks the hunt for a missing dance partner. Flashy clothes suggest a dubious lifestyle.
Meanwhile Superintendent Hazard (Nigel Patrick) and Inspector Learoyd (Michael Craig) call on the Harris family: David lives with his father (Bernard Miles), mother (Olga Lindo), sister Mildred (Yvonne Mitchell), and Mildred's young twin daughters. Sapphire had visited the family on Saturday morning and told them that she was pregnant. The father reluctantly agreed to a marriage - the family knew that Sapphire was coloured - but has a reputation as a racist, as does his daughter. The whole family fear the social consequences of their association with Sapphire, and Mildred's daughters have already been excluded from a friend's home.
Visiting an upmarket club for young, well to do black people, the police discover Sapphire preferred the racier environment of the Tulip club, where she began dating someone called Johnny. Many of the witnesses questioned by Hazard and Learoyd resent Sapphire either because she passed for white or because she is discovered to be coloured.
Pursued through the streets, Johnny is refused help or shelter and battered by racist Teddy boys. Brought in by police, Johnny's room is searched, and a bloodied shirt and flick knife are found. Johnny claims he had a fight with another club regular, Horace Big Cigar.
Meanwhile David's alibi is beginning to crack. He arrived back in London earlier than he claimed, and acted suspiciously on Hampstead Heath after the murder. Doctor Robbins is brought to the Harris house, much to the disgust of the family. Finally, Mildred explodes with racist venom, revealing her pathological hatred of black people and incriminating herself as the murderer, trying – as she saw it – to save the family from disgrace, spurred by Sapphire's taunting about the race of the baby she was carrying.
Opening as a routine whodunnit Sapphire is an interesting look at racial tensions in 1950s London, often with surprising subtlety, revealing not just underlying insecurities and fears of ordinary people, but that racism can be a two-way street. One man (the barrister son of a black African bishop) says his father would never have allowed him to marry Sapphire because she was partly white (his new black girlfriend calls Sapphire 'trash'). Other black characters are scornful of her passing as a 'lily-skin'.
The film ramps up the tension with well-paced revelations about Sapphire's life. Sapphire is at first assumed to be white, so the appearance of her black brother Dr Robbins (Earl Cameron) is genuinely astonishing, provoking reactions ranging from reluctant to downright hostile from those he meets, and ultimately exposing the real killer. Acts of politeness, such as an apology by a small child on a scooter to Dr Robbins, are very few and far between and bring the only light to what is a very dark, even grim, film.
One of the two detectives handling the case, meanwhile, has to confront his own prejudices. Nigel Patrick's Superintendent Hazard seems to genuinely accept people on their own terms, refusing to allow his handling of the case be swayed by racism or bigotry. His assistant, Learoyd on the other hand, does not. Sapphire's colourful dancing dresses are, for him, evidence of "the black under the white". When Sapphire is shown to be pregnant and to have black parentage, his immediate reaction is that the child's father “could be anybody”, because Sapphire would obviously be promiscuous. Visiting the doctor Sapphire consulted (Basil Dignam) Learoyd is brought up short when he says the doctor could surely have been able to tell Sapphire was coloured. The doctor immediately retorts that he couldn't tell Learoyd was a policeman because he didn't have big feet. Even as the case comes to its conclusion, Learoyd is still saying that “spades” (the n-word appears in the film, too) should just be sent home. Hazard says maybe they should also get rid of little old ladies who are prone to having their handbags stolen.
It is easy to criticise attitudes from the past, but Sapphire does make some effort to be thoughtful about race ("We plan to show this prejudice as the stupid and illogical thing it is" said Dearden), while remaining an absorbing detective story. It was made shortly after the 1958 Notting Hill race riots, before London began 'swinging' in the more permissive 1960s. As such, it is an interesting look at a grimmer, greyer London (nicely shot in colour by Harry Waxman), just emerging from post-war austerity into middle-class affluence and a multi-cultural society, wondering where this new world would lead. Voted Best British Film at the 1960 BAFTAs.