One Night With a Prince (Royal Brotherhood, Book 3)

Continuing her irresistible Royal Brotherhood Series, bestselling author Sabrina Jeffries introduces the third of three half-noble half brothers -- the brashest rogue in all of London.
Proper Lady Christabel, the Marchioness of Haversham, is desperate to regain some letters that could destroy her -- so desperate that she pretends to be the mistress of notorious gaming-club owner Gavin Byrne to accompany him to a scandalous house party where she can reclaim them. But when she agreed to let Byrne coach her on how a true mistress behaves, she never suspected how very...persuasive his wicked lessons would be.
Gavin is secretly determined to find the letters himself and use them for revenge against the noble sire who abandoned him to grow up in London's worst slums. He's also delighted at how very successful his "mistress lessons" are: it won't be long before the luscious young widow is in his bed. But when Christabel catches Gavin in his own seductive net, he faces a difficult choice: to wreak the vengeance he's planned all his life, or to protect the woman he may -- to his own astonishment -- need more than revenge.