Only a Duke by Tanya Wilde

A bright heiress. A cold investigator duke. And a family feud that could ruin them both.
Lady Louisa Talbot has three rules when it comes to men: avoid fortune hunters, avoid criminals, and most importantly, avoid powerful men. Especially dukes. Dukes are the worst! So imagine her shock when she catches one rifling through her drawers in the dead of night. And this is not just any duke—he’s her family’s sworn enemy!

Oliver Cavanagh, the Duke of Mortimer, is ruthless, calculating, and never fails to bring an opponent to heel. So sneaking into a Talbot residence to retrieve useful evidence should be a mere trifle. Until getting caught red-handed by a very cross, very alluring Lady Louisa turns the whole situation highly inconvenient. Worse, the item he is after has vanished, stolen away by a band of suspicious brothers from Brighton. Now he has no choice but to track it down yet again—except Lady Louisa refuses to be left behind.

With every perilous twist, sparks fly, and Oliver finds himself impossibly drawn to the one woman who threatens his ironclad control. But he also harbors a secret—one that could shatter the tenuous alliance that has grown between them.