One Night with a Prince by Sabrina Jeffries

Lovely Christabel, the Marchioness of Haversham, is desperate to regain some personal correspondence—so desperate that she pretends to be the mistress of notorious gaming club owner Gavin Byrne, in order to attend a scandalous house party hosted by the man holding her letters. But when she agreed to let Byrne coach her on how a true mistress behaves, she never suspected how very… appealing his wicked lessons would be.

Secretly determined to find the letters before Christabel, so he can use them to avenge a childhood tragedy, Gavin can’t help but be delighted at his pupil’s performance with regard to his “mistress lessons.” It won’t be long before the luscious widow is in his bed. Ultimately, though, will love or revenge triumph?