Scandalous - The Abcynians, #4

The Royal Advisor to the King of the Abcynians, Nicholas, Duke of Arrington, is inscrutable, lofty, and elusive. A widower with two grown sons and no intention of remarrying, he never expects to meet Miss Regan Saunders while walking through Parade Gardens. Aware that she's his destined mate, he's fascinated. For not only is she prepared to push the boundaries of society's expectations of a gentlewoman to become a doctor, she's an Abcynian Guard, therefore, capable of protecting his and his family's secrets.
Due to horrific betrayal by his first duchess, he believes it's best to court her with the utmost discretion to avoid a scandal that could lead to her ruination. Nevertheless, when Regan becomes the target of a macabre killer, Nicholas will stop at nothing to protect her, including marriage. Despite the rushed circumstances, it isn't long before they open their hearts, falling in love, neither aware that an assassin has been plotting with an ancient adversary to destroy the Abcynians for centuries.
To expose the truth, they'll risk everything they hold dear to stop a predator before it's too late.