On 3 July 1930, a maid discovered the dead body of her employer on the floor of the sitting room in an upmarket apartment in Temple, London. The victim was 37-year-old Sidney Russell Cooke, mysteriously shot through the stomach by a hunting rifle. He was the husband of Titanic Captain Edward Smith’s only daughter, Helen, known to friends as ‘Mel’. Unknown to many, he was also an MI5 spy, described as a ‘prototype James Bond’ - and the esteemed Cambridge economist John Maynard Keynes’ lover...