The Nation's Missing Guest (an Amos Lee Mappin Mystery) - Footner Hulbert

Sheik Ahmed bin Said arrives in the United States with his British bride-to-be and her overbearing mother, amid political machinations between France and Britain as they jostle for control of his country, Shihkar, and plotting by his devious stepbrother. Ahmed asks his old Oxford chum, Luke Imbrie, to travel to Washington DC with him as he performs his political obligations, but chaos ensues when Ahmed (and a million dollars in jewels) disappears from the train. Author and investigator Amos Lee Mappin is called in investigate, following twists and turns as he examines suspects while directing the search for the missing Sheik. The Nation's Missing Guest was published in 1939.