The Queen of Attolia - Megan Whalen Turner (Book 2 in the Queen's Thief series)

When Eugenides, the Thief of Eddis, stole Hamiathes's Gift, the Queen of Attolia lost more than a mythical relic. She lost face. So when Eugenides taunts her by brazenly breaking into her stronghold one more time, she is willing to do anything - even risk her country - to execute the perfect revenge .