The other novels bearing the subtitle "A Problem in Deduction" are The Roman Hat Mystery (1929), The Dutch Shoe Mystery (1931), The Greek Coffin Mystery (1932), The Egyptian Cross Mystery (1932), The American Gun Mystery (1933), The Siamese Twin Mystery (1933), The Chinese Orange Mystery (1934), The Spanish Cape Mystery (1935), Halfway House (1936), The Door Between (1937), The Devil to Pay (1938), The Four of Hearts (1938), and The Dragon's Teeth (1939). They resemble The French Powder Mystery in their emphasis upon the puzzle, upon order and social decorum, and upon the importance of plot rather than character.