The Guarded Heart by Barbara Hazard.
A romance novel set in Regency England, although most of the action takes place in Vienna, which is a change of pace. Erica Stone goes to Vienna to find her cheating husband, only to discover he has been murdered. The Duke of Graves enlists her as a spy for England, and even though she is terrified of him, eventually they fall in love. He has a club foot. The writing is pretty good for a romance, but the devo factor is low, because the Duke’s disability is relatively minor and doesn’t end up factoring into the plot very much, and because he is an aloof, controlling jerk right up to the inevitable happy end.