Heir of Fire is the third book in the Throne of Glass series (not counting the novella bind-up) by Sarah J. Maas. If you don't know what the series is, let me give you a synopsis of the first book (this is from goodreads):
"After serving out a year of hard labor in the salt mines of Endovier for her crimes, 18-year-old assassin Celaena Sardothien is dragged before the Crown Prince. Prince Dorian offers her her freedom on one condition: she must act as his champion in a competition to find a new royal assassin. Her opponents are men-thieves and assassins and warriors from across the empire, each sponsored by a member of the king's council. If she beats her opponents in a series of eliminations, she'll serve the kingdom for three years and then be granted her freedom."
If that doesn't interest you, I can promise that the series takes way bigger problems than this, but you have to start small, you know? If you are looking for a solid fantasy series, this is for you. Now, if you've read Crown of Midnight, the second book, and haven't picked up this one, what are you waiting for? Do it. If I were to sum up this book in one word, it would be "epic". We get a much larger view of what's going around. With new characters, new perspectives, new lands, new creatures, and new revelations, this book sets us up for what seems to be an action-packed and emotion-filled heck of a journey for our main character, Celaena Sardothean.
DO NOT SCROLL DOWN IF YOU HAVE NOT READ THE BOOK.