In the Hand of the Goddess - Tamora Pierce - Bog

"Alanna, disguised as a boy, becomes squire to none other than the heir to the throne. Prince Jonathan is not only Alanna's liege lord; he is also her best friend--and one of the few who know the secret of her true identity. But when a vicious sorcerer threatens the prince's life, it will take all of Alanna's skill, strength, and magical power toprotect him--even at the risk of surrendering her dreams."--