The Assassin and the Underworld by Sarah J. Mass

The Assassin and the Underworld (Throne of Glass, #0.3) - Sarah J. Maas

Celaena returns from the Desert and is determined to leave her master and Assassin’s Guild to start the life on her own. But Arobynn offers her an assignment Celaena can’t refuse - she must kill the man who wants to trade slaves with the kingdom. I liked this short story the least - it was just too predictable and it was hard to read how naive Celaena was. I totally saw it coming, I knew exactly how this story will end. Celaena really starts to show her flaws. She’s too trusting sometimes and even when she constantly repeats how great and pretty she is, deep down she’s actually very insecure. She’s grown fond of Sam, but she just can’t stop being rude to him. These faults gave her personality more depth and it really made me love her as a character.

Source: http://thetemporaryescape.blogspot.com/2013/09/mini-reviews-prequels-to-throne-of.html