One for the Rogue by Charis Michaels

Beauregard “Beau” Courtland has no use for the whims of society and even less for aristocratic titles. As a younger son, he travels the world in search of adventure with no plans to settle down. Even when the title of Viscount Rainsleigh is suddenly forced upon him, he will not bend to duty or decorum. Not until an alluring young woman appears on the deck of his houseboat, determined to teach him propriety in all things and tempting him with every forbidden touch…

Lady Emmaline Crumbley has had a wretched year. Her elderly husband dropped dead without naming her in his will and she’s been relegated to the life of a dowager duchess at the age of 23. She has no wish to instruct a renegade viscount in respectability, but desperate to escape her greedy stepson, Beau’s family makes her an offer she cannot refuse:  teach the new lord to behave like a gentleman, and they’ll help her earn the new, self-sufficient life of her dreams. Emmaline agrees, only to discover that instructing the viscount is one thing, but resisting him is quite another. How can she teach manners to the rakish nobleman if he is determined to show her the thrill of scandal instead?