Communing with Mr. Quin: The Soul of the Croupier by Agatha Christie

Are you ready for an oh-so-European tale of despair, betrayal, and
misplaced pride? Would it help if you listened to some Edith Piaf
while we told it to you? Okay, then. Time to sit for another
soulful spell with Mr. Harley Quin and his dessicated sidekick, Mr.
Satterthwaite, this time on the shores of Monte Carlo. Bon voyage!