•Why it earns a slot
Why it earns a slot: it is the book that invented the modern conspiracy-thriller machinery, a secret society with rules, cards, and a president, decades before genre fiction made that a formula, and Stevenson wraps it in the mock-Orientalist framing device of the title itself.
A prince slumming incognito through London nightlife stumbles into a club that exists to arrange its members' suicides by playing cards, and Stevenson spins the premise into six interlocking tales of disguise, murder, and blind luck.
This distillation is written from the freely available original, which is always the better read when you have the time: Project Gutenberg.