The body of a woman is found in a corner of Hampstead Heath. She's been strangled, and it's clear from her appearance that she was a prostitute. The detectives seem faced with a hopeless lack of evidence. They have a suspect and several contradictory witnesses, but no proof and little information to go on. With ingenuity and tireless patience Inspector Poole of Scotland Yard finds out that the dead woman was not always a low-grade prostitute but had sunk to hopeless poverty from a very different life.