Countdown (The 39 Clues: Unstoppable #3) by Natalie Standiford
Publisher: Scholastic Inc.
Goodreads Summary: The clock has finally run out for the Cahills. As the leaders of the world’s most powerful family, Dan and Amy have been in the crosshairs for too long. It was only a matter of time until luck failed them.

Media tycoon and presidential candidate J. Rutherford Pierce has set his sights on destroying the siblings. And after numerous close calls, it looks like he’s about to get his wish.

Now Dan is hopelessly trapped and nothing can save him. Nothing except unleashing an evil the Cahills have spent centuries trying to hide.

The Cahills have always had a secret weapon, but it comes at a great cost. With everything to lose, Amy has to ask herself the question that haunts her nightmares:

Just how far is she willing to go to save her little brother?

Rating: 5 Stars
Review:  This book is just stunning. Amy's sacrifice, and her desire to protect Dan just add to the power of the story. Amy, Dan, Jake and Atticus continue their search for the ingredients of the antidote to the serum. Meanwhile, J. Rutherford Pierce is even more determined to kill them, although not desperate. Amy and Dan discover Pierce's wife's true identity, and overcome obstacles in their way. This is Amazing. Natalie Standiford uses Amy's desire to protect to make the story sadder, and just more brilliant. Countdown really is fantastic, and sacrifices must be made or all will be lost.
Purchase Location: Borrowed From Library
Edition: Hardcover
Buy the book: Book Depository
Recommended for: Fans of challenges, choices, and consequences, action.