Pistols at Dawn (Intrepid Heroines #4)
Andrea Pickens

But her mistaken accusations result in grave injury to the earl's nephew. Now Eliza's sister—a noted healer—feels obliged to nurse the young man back to health, and Eliza has no choice but to help.
Killingworth is not pleased with the arrangement. Tensions swirl between the four of them, until new bonds are discovered when evil strikes again and they must work together to fight a relentless enemy, who will stop at nothing to drive Killingworth away from his estate.