Tear Down the Throne by Jennifer Estep

Bestselling author Jennifer Estep continues her Gargoyle Queen epic fantasy series where magic reigns, alliances are tested, and a dangerous attraction could tear down a throne. . .

Crown princess. Clever spy. Powerful mind magier. Gemma Ripley of Andvari is all those things—and determined to stop an enemy from using magical tearstone weapons to conquer her kingdom.
Gemma’s quest for answers leads her to a trade Summit between the various kingdoms. Among the other royals in attendance is Queen Maeven Morricone of Morta and her son, Prince Leonidas—Gemma’s charming and dangerous nemesis.
Gemma knows that Maeven always has a long game in motion, and sure enough, the cunning queen invokes an arcane tradition that threatens the fragile truce between Andvari and the other kingdoms. Despite her best intentions, Gemma once again finds herself thrown together with Leo and battling her growing feelings for the enemy prince.
When a series of deadly attacks shatters the Summit’s peaceful negotiations, Gemma realizes that someone wants to tear the royals down from their thrones—and that this enemy just might succeed.