He is best remembered for his 1902 novel of courage and cowardice in wartime, The Four Feathers, and is also known as the creator of Inspector Hanaud, a French detective who was an early template for Agatha Christie's famous Hercule Poirot.

His prolific output in short stories and novels were frequently made and remade into films during his lifetime; though many of the silent versions have been lost or forgotten, the productions of Fire Over England (1937) and The Four Feathers (1939) remain enduring classics of British cinema.

He wrote, "I had three plays produced by George Alexander; one a failure, Colonel Smith, one which made a moderate profit, Open Windows, and one which was a considerable success, The Witness for the Defence.

[14] 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.

[15] 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.

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.

A thinly veiled metaphor for then-neutral Britain's need to prepare for the threat of Nazi invasion, and published while the Spanish Civil War was raging, the book was adapted for film by the author Clemence Dane for Alexander Korda, England's leading film producer; Korda was helping Winston Churchill in his struggle to alert the British people to the military threat of the Third Reich.

[18] The lavish costume drama also made stars of Vivien Leigh and Laurence Olivier in their first pairing as lovers onscreen, as they were off-screen.

Released before Britain's entry into World War II, its pro-British theme also features valiant British fighting against hopeless odds, this time in a late 19th century imperial setting.