In the short story The Soul of the Croupier, Countess Czarnova is someone that Mr Satterthwaite had seen on many occasions during his summer hoidays in Monte Carlo. Like Satterthwaite, she frequented the place. He had once seen her accompanied by a Grand Duke, and then an Austrian Baron. "In successive years her friends had been of Hebraic extraction, sallow men with hooked noses, wearing rather flamboyant jewellery. For the last year or two she was much seen with very young men, almost boys."
According to Franklin Rudge who was attracted to her, the Countess was a Radzynski, one of the oldest families in Hungary. It was said that she had been a mistress of the King of Bosnia. He had given her a large necklace of pearls after she helped smuggle some secret papers out of the kingdom for him. She was apparently no stranger to diplomatic intrigues.
Satterthwaite observed that the Countess gave Rudge, a young American, "a glimpse, so the young American was made to feel, into the life of the old regime with the Countess as the central figure, aloof, aristocratic, the friend of counsellors and princes, a figure to inspire romantic devotion."
The countess had however a more complex backstory, and this would form part of the surprise delivered by the plot.