Here is another amazing book by Sarah J. Maas. I actually couldn't wait long enough for the library to get the book so I paid sooooo much money to get it the minute it came out... and I have no regrets. I have read the book 3 or 4 times since I got it and then I lent it to a friend and she returned it only to beg for it back so she could read it again. All in all, this is one of Sarah J. Maas's best books in the series so far.
I am not going to explain the book seeing as it is the 5th book in a series, but I HIGHLY recommend you go check out the first book in the series called "Throne of Glass". I wouldn't recommend this book for anyone under 15 as it does deal with mature subject matter (if the main character being an assassin doesn't tell you enough).
Check out "Throne of Glass" here: http://www.goodreads.com/book/show/7896527-throne-of-glass