A shining star in a great series.

The story:
Picking up years after the last time we saw Allie and Aidan, their lives are very different. They haven't seen each other since Aidan left for Germany. Allie still hurts from his abandonment but she has Darius, Aidan's brother and her other half. She should be moving on. Just when she begins to think she is, she finds out Aidan is missing and that she has a bigger role to play than she thought. 
What I loved: Just about everything. This is by far the best in the series which is strange because Allie and Aidan are at odds for most of it. But her platonic relationship is truly special to watch and I really enjoyed seeing that develop without Aidan there to cause conflict. 
The cast of characters we've come to know is just as lovable as always. I really loved getting to know her grandparents - the ancient queen and scholar. And the sisterly bond with Livia that has developed is really a strong point. 
The story in this series has always been good, but it's been the characters that keep you glued to the page and that is especially true with the Heir.

What was just okay:
I suggest reading this right after the previous book or else the beginning takes a bit to get into. It's such a complicated world that it's hard to straighten everything out right away if it's not fresh in your mind. 
I spent most of the book hating Aidan, but I think I was supposed to in order to really feel his struggle - which I did. 

Final Verdict:
A fantastic story with characters who reach right out of the story to grab you and never let go. This is not a book I'll soon forget. I can't wait for the next one.