A Duel of Jewels — Barbara Cartland

Betrothed against her wishes to an elderly Duke, Katerina left her French stepmother's home. Katerina fled, and while in exile, she met her neighbour, the dashing Prince Michael and was befriended him. But the Prince Michael was a man determined to win a wager against the evil Prince Fredrich. And true love never runs smoothly, however, and soon both Michael and Katerina are in mortal danger.