The Assassin's Blade (Throne of Glass, Prequel Novellas)

Celaena Sardothien is her kingdom's most feared assassin. Though she works for the powerful Assassin's Guild and its scheming master, Arobynn Hamel, she yields to no one and trusts only her fellow killer-for-hire, Sam. But when Arobynn dispatches her on missions that take her from remote islands to hostile deserts, Celaena finds herself acting independently of his wishes and questioning her own allegiance. If she hopes to escape Arobynn's clutches, Celaena will have to put her faith in her wits and her blade knowing that if she fails, she'll lose not just a chance at freedom but her life.