Historical Fiction:
* The Scarlet Pimpernel (1905): This novel, a classic of the genre, tells the story of an English aristocrat who secretly rescues French aristocrats from the guillotine during the French Revolution.
* The Man in the Iron Mask (1908): This novel tells the story of a mysterious prisoner kept in an iron mask at the Bastille prison, and has been adapted numerous times for the screen.
* The Black Douglas (1912): This novel tells the story of the famous Scottish warrior, William Douglas, who fought against the English in the 14th century.
* The Last Crusade (1918): This novel tells the story of the final Crusade, led by King Louis IX of France, in the 13th century.
Nonfiction:
* The Story of the Scarlet Pimpernel (1924): A detailed account of the origins and development of the character of the Scarlet Pimpernel.
* The Romantic Movement in English Poetry (1931): A critical study of the Romantic poets, including William Wordsworth, Samuel Taylor Coleridge, and Percy Bysshe Shelley.
It is important to note that while some sources list C.H. Stuart Duncan as the author of "The Scarlet Pimpernel" and "The Man in the Iron Mask," these novels were actually written by Baroness Orczy. There seems to be some confusion about the authorship of these works, possibly due to the fact that Stuart Duncan wrote a number of other popular historical novels that were well-received by the public.
Regardless of the confusion, C.H. Stuart Duncan was a prolific writer who left a lasting legacy on the world of historical fiction.