The Assassin's Blade: The Assassin And The Pirate Lord By Sarah J. Maas

 16 year old Celaena is up late at a meeting of Assassins and just found out that the Head of Council's second in command Ben was killed.  Calaena was Ben's protegee.  When she goes with another assassin to see the body of her mentor, things go wrong including boats full of slaves and an awful pirate lord.  She will have to bring the pirate lord down to save many others.

I recommend this story to anyone who likes thrills, mystery and a good story.