Winds of the World by Talbot Mundy

Beyond question Yasmini is a craftsman of amazing skill, and her genius--as does all true genius--extends to the almost infinite consideration of small details. The medium in which she works--human weakness--affords her unlimited opportunity; and she owns the trick, that most great artists win, of not letting her general plan be known before the climax. Neither friend nor enemy is ever quite sure which is which until she solves the problem to the enemy's confusion.

But Yasmini could have failed in this case through overmuch finesse. She was not used to Germans, and could not realize until too late that her compliance with this man's every demand only served to make him more peremptory and more one-sided in his point of view. From a mere agent, offering the almost unimaginable in return for mere promises, he had grown already into a dictator, demanding action as a prelude to reward. He had even threatened to cause her, Yasmini, to be reported to the police unless she served his purpose better!