Agatha Christie's The Secret Adversary
Christie changed her writing style a lot over the decades a lot of her early books like Murder on the Links, Brown Suit, and The Secret at Chimneys are more spy thrillers and charming adventures though they have mystery elements.
Tommy and Tuppance play well as a dime store adventure and thats charming to someone who enjoys this sort of story
Still Incan see why Mysterious Affair, Adversary, and Brown Suit are just not as well remembered or adapted
Tommy and Tuppance
Still Tommy and Tuppance is exactly the style and feeling I would want to hit for a 1920s ttrpg like I have always wanted to do with Adventure! The problem is finding players who want to do that style is hard