I recommend this book for: high school
In a world where some people are born with Graces - special gifts for anything from baking to mind-reading to predicting the weather - Katsa serves her uncle, the king of the Middluns. Her Grace is fighting, and she uses it at the king's command to threaten, hurt, or kill his enemies - or sometimes just subjects who have ticked him off. She despises herself for it. But Katsa has a secret - the Council, a group that she and sympathetic friends have started to fight the kinds of abuses she herself is forced to lay on the common people. It is on a Council mission that she meets Po, the prince of another kingdom - and another Graceling fighter. His grandfather has been kidnapped and they have to find out why, because it could have ramifications not just for his family, but for all of the seven kingdoms.
This book blew me away. The world was original and lovely, and Katsa was a fantastic heroine. She grows a lot during the course of the book, but she has certain principles that she holds to and will not sacrifice. The development in the other main characters was also great. The ending wrapped up a little too quickly for me, but the story was definitely well-plotted. As in real life, there were no easy answers about why the villain is doing what he does. The love story was completely engrossing. Definitely one of the better fantasies I've read!
If you're concerned about mature content, highlight starting here: There is sex in this book! One scene makes it very clear what is happening, and there are a few other references to lovers sharing a bed and some innuendoes. A medicinal form of birth control is used - I know that might reassure some parents and offend others, so I thought I'd bring it up. The villain is a very bad man who takes pleasure in the pain of others - the book describes how he cuts up animals, hurts servants, and it is implied that he wants an inappropriate relationship with his daughter. End of invisible text.