United as One by Pittacus Lore

Summary: "The seventh and final book in the #1 New York Times bestselling I Am Number Four series! With United as One, this action-packed series comes to a surprising, breathtaking, and utterly satisfying conclusion. The Garde didn’t start this war, but they’ll do whatever it takes to end it once and for all. . ."

I can't believe this series is over. 

It's been a part of my life for almost 5 years now, and I don't want it to end! 

The Garde finally have their ultimate knock-down, drag-out showdown with the Mogs. The battles were more intense than I ever expected. I was crying and freaking out for a large portion of the book. 

No other book series has quite matched the level of teamwork and ragtag family vibes as the Lorien Legacies. I wish more book series developed this level of friendship and value among its characters. It's truly a special reading experience. 

For your reference, the book order goes:

I am Number Four
The Power of Six
The Rise of Nine
The Fall of Five
The Revenge of Seven 
The Fate of Ten
United as One

There are also many short stories and "lost files" that supplement the books (I haven't read those). 

467 pages