Lady Charlotte Always Gets Her Man by Violet Marsh

Family secrets, a brother's best friend's romance, and scandalous mystery combine in this delightfully witty historical rom-com—perfect for fans of Evie Dunmore, Enola Holmes, and Netflix's Bridgerton!
Lady Charlotte Lovett should have never run away upon discovering her betrothal. But when one has been promised to a man who, rumor has it, killed his previous two wives, one does what one must. The only thing that can get her out of this engagement is proving that Viscount Hawley is as sinister as she thinks he is. And the person who would know best is his very own brother.
In many ways, Dr. Matthew Talbot is the exact opposite of his sibling—scholarly, shy, and shunned by society. But like his brother, he has secrets, and he doesn't need Charlotte exposing them in her quest to take down the viscount. It only seems prudent to help her while keeping her from poking her nose in all the wrong places. But as they put their hearts at risk to grow closer to each other, they are also getting closer to a dangerous confrontation with Hawley.