The Traitor's Ruin by Erin Beaty
After proving her worth in book one as a deft spy and strategic matchmaker, Sage Fowler is now comfortably positioned in high society as the royal tutor. When she's called upon to teach his majesty's soldiers how to read and write, she jumps at the chance to serve her kingdom of Demora - and to be reunited with her fiance, Captain Alex Quinn. During a skirmish, Sage and Alex are separated. She watches him die before he can deliver important military intel - or so she thinks. She escapes from the enemy and makes an unlikely alliance with a mysterious soldier from a third nation. As Sage tries to rally their support against a common foe, the important political alliance is plagued by secrets and betrayal. Can Sage complete Alex's mission and save her kingdom once more?