More like The Big Four

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Barney CusterSeries
series3 books1914
completed
Thriller & suspense, adventurous and tense in tone, about political intrigue, set in early 20th century and europe.
“Barney Custer is an American farmer from Nebraska who travels to the small European kingdom of Lutha only to discover he's the spitting image of its unstable ruler, King Leopold.”
from the catalogue
Start with The Mad King →
SS-GBNovel
Len Deightonstandalone novel1978
Alternate history and spy thriller, about murder investigation, set in big city.
“Archer's investigation collides with occupation politics, the British resistance, and rival factions of the SS and the German Army, each wanting the case to go a different way.”
from the catalogue
FatherlandNovel
Robert Harrisstandalone novel1992
Alternate history, about totalitarianism and murder investigation, set in mid 20th century.
Hercule PoirotSeries
series9 books1923
completed
Mystery & detective and thriller & suspense, adventurous and tense in tone, about political intrigue, set in early 20th century and europe.
Start with The Adventure of the Egyptian Tomb →
The Thirty-Nine StepsNovel
John Buchanstandalone novel1915
Adventure and spy thriller, about survival.
The War in the AirNovel
H. G. Wellsstandalone novel1908
Science fiction and military science fiction, about war, set in our world.