Witness for the Defence opened on 1 February 1911, starring Sir George Alexander as Henry Thresk. In 1913 Mason's problem play Open Windows opened on the evening of 11 March, starring Sydney Valentine as Phillip Hammond, Irene Vanbrugh as Cynthia Herrick, Sir George Alexander as John Herrick, with Rosalie Toller as Elsie Herrick. Mason served with the Manchester Regiment in the First World War, being promoted Captain in December 1914. He transferred to the General List (reservists) in 1915 and the Royal Marine Light Infantry in 1917 with the rank of Major. His military career included work in naval intelligence, serving in Spain and Mexico, where he set up counter-espionage networks on behalf of the British government. Mason turned to non-fiction as well; he wrote a biography of Sir Francis Drake (1941), whose piratical exploits for the Queen figure in Fire Over England. He was working on a non-fiction book about Admiral Robert Blake when he died in 1948. Mason had been offered a knighthood but reportedly declined it, declaring that such honours meant little to a childless man. Works Mason's prolific output included over 30 novels as well as plays, short stories and articles. Many of his novels were adapted for the screen, several multiples times. During the 1910s and 1920s he worked closely with many film directors of the silent era. Inspector Hanaud In 1910, Mason undertook to create a fictional detective as different as possible from Sherlock Holmes, who had recently been resuscitated after his supposed death by Arthur Conan Doyle in 1903. Inspector Gabriel Hanaud was stout, not gaunt like Holmes; a professional policeman, not a gentleman amateur; from the French Sûreté, not Victorian England; and relying on psychological insights rather than physical evidence. His "Watson" is a retired London banker named Mr. Julius Ricardo. Hanaud's appearance in the 1910 novel At The Villa Rose marks "the first major fiction detective of the Twentieth Century," according to a historian of the genre. Set in the south of France, its plot also ridicules spiritualism and mediums, well-known enthusiasms of A. Conan Doyle. Four more Hanaud novels and several short stories followed, the last, The House in Lordship Lane, in 1946 and the only one set in England. The first Hanaud book was a best-seller, as were several of his 30 novels, and as such often adapted into films, often more than once. A 1920 version of At