A Dark Gentleman by Frances M Carr

Mysterious strangers can often be dangerous. Sarah Littlejohn's heart skipped at the prospect of joining her Aunt for a London season, for at one and twenty Sarah was no longer a young girl. A mishap on the journey brings her face to face with Jack Edgeworth who she blames for the accident. Jack finds her disapproval amusing, but he is less amused when she attracts the attentions of the handsome Robert Rossingham. As Aunt Charlotte observes, Sarah must learn to tell the sheep from the wolves, but that proves to be far from easy.