Let Me Be Your Hero by Courtney McCaskill

Being ruined is the least of Isabella Astley’s problems.

Visiting the Dark Walks of Vauxhall seemed like a harmless adventure at the time. But ever since Lady Isabella overheard men plotting treason, someone has been trying to kill her!
Her only hope is Archibald Nettlethorpe-Ogilvy, a rich industrialist and engineering savant. Archibald fell hopelessly in love with Isabella the moment he clapped eyes on her. He has been scorned by so many women for being in trade that he knows such an ethereal beauty could never come to care for the likes of him. But now her life is in danger, and he happens to be one of the few men with enough wealth and power to protect her. Seizing his chance, he proposes marriage, an offer Isabella has no choice but to accept.
Passion flares between these unexpected lovers. For Archibald, putting his life on the line to keep Isabella safe is the easy part. But showing the woman who could crush him with a word his heart, and his true self? That is more terrifying than facing a thousand hired assassins…

Please note that the heat level is red hot!