It is one of London's great unsolved mysteries. Late one evening in May 1957, an elderly Polish Countess was travelling home from a party when she was attacked at Gloucester Road Tube station. Stabbed repeatedly on the platform, she died in hospital later that night. Her killer was never identified and, to this day, there are only theories about why Countess Teresa Łubieńska was targeted. But could there be a clue in her past? The Countess had a remarkable life. She was a film-maker, an activist, a poet, a resistance fighter and a concentration camp survivor. She was an extraordinary woman. And somebody wanted her dead.