This late novel of E. Phillips Oppenheim begins as the Train Bleu pulls into the railroad station in Monaco.
Its a leisurely spy fiction tale set in Monaco as various members of aristocracy from different countries plus one vacationing American woman find themselves involved with international intrigue. The bulk of the book consists of members of the leisure class drinking cocktails, playing baccarat, and generally spending time in Monacos elite clubs.
In the late 1930s, Oppenheim was living in the South of France, near Monaco, as that playground of the wealthy slowly emptied out it wealthy and royal clientele in advance of the coming war.