Guardian's Compact Series by Sabrina Chase

Her great-uncle, the mage Oron, bequeathed to her his oak-shaded chateau and a debt of magical honor. But Miss Ardhuin Andrews must hide her magical talents. How can she repay the debt? Political intrigue, duty, and echoes of an old war not truly ended combine to create a smoldering crisis in a world where magic and science coexist.

Only one Mage Guardian now defends Aerope from the malevolent plans of Denais and his dreams of conquest and revenge. Ardhuin desperately tries to make the Allied governments see the danger and replace their murdered Guardians, but the long peace dulls any sense of urgency. Her new husband Dominic fears the Allies consider Ardhuin's phenomenal power sufficient—and in no need of help from their mages. And yet.. moreOnly one Mage Guardian now defends Aerope from the malevolent plans of Denais and his dreams of conquest and revenge. Ardhuin desperately tries to make the Allied governments see the danger and replace their murdered Guardians, but the long peace dulls any sense of urgency. Her new husband Dominic fears the Allies consider Ardhuin's phenomenal power sufficient—and in no need of help from their mages. And yet...a weary traveler from the ends of the earth rushes to their home to deliver a message from a man thought dead. A desperate plea for help, invoking the Compact—as only another Mage Guardian would. Does another survive after all? And what new danger threatens the world? less