Sarah J. Maas 
Assassin and the Empire [EPUB ebook] 
A Throne of Glass Novella

One final mission could be the beginning…or the end. Celaena Sardothien is the assassin with everything: a place to call her own, the love of handsome Sam, and, best of all, freedom. But Celaena won’t be truly free until she is far away from her old master, Arobynn Hamel-so she and Sam decide to take a last daring assignment that will liberate them forever. And that’s how Celaena learns that having everything means that everything can be taken away.