On the morning of Monday 10 September 1923, a mysterious woman in black, known as 'the Princess Fahmy Bey', was escorted to the dock of London's central criminal court to face a charge of murder. Two months before at the Savoy Hotel, the princess had shot dead her husband, an Egyptian prince, with three bullets, in cold blood. Six years before, she'd had a secret affair with another prince: the future Edward VIII. Back then the Princess Fahmy Bey had been plain Marguerite - or Maggie - Meller, a high-class courtesan in First World War Paris. As Maggie Meller went on trial for her life, this reckless episode from Edward's past threatened to expose the heir to the British and imperial throne to disgrace. Behind the trial lies a long-buried story of royal infatuation and royal scandal. Edward's affair with Maggie Meller finally exploded in a toxic cocktail of sex, blackmail and murder. New evidence, unearthed over a decade of investigation by the historian Andrew Rose, points to it ending in an establishment cover-up to protect the reputation of the future king and save his first, secret mistress from the gallows.