The Fire's Stone by Tanya Huff

It was a long fall from Clan Heir to common thief, but Aaron never wanted any part of his father's brutal outlander reign. In fact, besides coin purses and jewels, there's very little in all of Cisali that interests Aaron, until he stumbles—quite literally—into a prince's bedchamber...

Prince Davish of Ischia is a skilled swordsman both on the field and beneath the sheets, at least when he isn't outrageously drunk. But the wine helps him forget all the ways he's disappointed his father, his family, and soon enough, his young bride-to-be...

A trained Wizard of the Nine with more raw talent than real-world experience, Princess Chandra has no interest in the politically arranged marriage. She flees to the royal city of Ischia seeking a way out of the union. But there, she discovers something far more shocking than Prince Davish's rakish reputation...

The Stone of Ischia has been stolen. A powerful talisman, The Stone protects the city from the active volcano that looms over...