The Duke's Indiscretion by Adele Ashworth

The famous soprano, Lottie English, is—unbeknownst to anyone—really the Lady Charlotte Hughes. Colin has been admiring Lottie from afar for almost three years when he finally decides to ask her to be his mistress. Instead, Lady Charlotte suggests they marry so that he can finance a European tour for her, and he can have her legally. Colin agrees, and soon discovers someone at the theater is trying to hurt her. But it's only when her dressing room is vandalized does Charlotte reveal that she possesses a rare, unpublished piece by George Handel that she supsects is the reason for all the violence. Fortunately, Colin secretly works for the government as a forger, and together they concoct a plan to set up the thief. As they work together, they discover true love in the face of danger.