Soon after embarking on a career as a writer, he published one of his most popular novels, The Lunatic at Large. He was also a historian, author of a great history of Orkney, a founder member and second president of the Orkney Antiquarian Society, and a Fellow of the Society of Antiquaries of Scotland. His The Spy in Black was made into a successful film in the late 1930s. His First Offence was also filmed in France as Drôle de drame (directed by Marcel Carné, 1937).
He died at home at Smoogro House, Orphir, Orkney.
Asked how to say his name, he told The Literary Digest it was cloos'-ton, "with ou as in group." (Charles Earle Funk, What's the Name, Please?, Funk & Wagnalls, 1936.)