Scotland Yard are investigating the murder of a beautiful young woman found stabbed on Hampstead Heath. Superintendent Hazard (Nigel Patrick) and Inspector Learoyd (Michael Craig) lead the investigation and quickly discover that Sapphire had been leading a double life, her light coloured skin allowing her to pass for white when in fact she was black. The police discover a motive for the murder when they discover that Sapphire was pregnant by her white boyfriend David Harris, a fellow student. Police enquiries lead them on a manhunt through both the black and white communities in London where they encounter distrust and racial prejudice. Whilst the chilling climax to this tense thriller illustrates how racial prejudice can tear apart even the most loving of families.