Graceling 

In a world where some have a Grace – a unique, uncanny, gift – Katsa's talent for killing makes her the king's perfect tool. But she chafes at being the king's thug. When she meets Prince Po, who has a Grace to match hers, she learns a new truth about her own Grace, and about a terrible secret hidden far away. "Vividly imagined... mesmerizing."—Booklist