The 39 Clues Series

The 39 Clues, Book 1: Maze of Bones by Rick Riordan

Taken simply as a story, this is pretty good. Sure, you have to park
your disbelief at the door and give up on any expectation of realism.
That done, it's loads of fun, with action, mysteries, and clues. It's
clearly intended to make money, and a little more baldly than most. But
as long as the writing is good and the story is fun, who cares? And Rick
Riordan, author of the Percy Jackson
series, knows how to pace a story.

 The 39 Clues, Book 2: One False Note by Gordon Korman

This installment keeps moving like the first -- from Vienna to Salzburg
to Venice this time. And it keeps you guessing about how the clues will
fit together. But the brother-sister team seems less likable here. Dan
won't stop whining about how boring he thinks Mozart is and the two
won't stock bickering. It overshadows their talents and makes you wonder
how they're able to stay ahead of the competition.

 The 39 Clues, Book 3: The Sword Thief by Peter Lerangis

This installment sends the Cahills to Japan and Korea and teams up Amy
and Dan with ruthless relatives Ian and Natalie Kabra. The book starts
and ends with fun flourishes and twists but it also gets to the heart of
what the four Cahill branches are really fighting over -- and it's not
all that original. Also, the puzzles leading to the clues are confusing
and the romantic subplot feels clumsily put together.

 The 39 Clues, Book 4: Beyond the Grave by Jude Watson

Dan and Amy Cahill work their way through Egypt in this installment.
Lucky for them their grandma has left numerous hints around Cairo and
the tombs. Once again this installment doesn't hold a candle to the
first in the series. There's no logical flow from one clue to the next
and the way the kids figure out some of the puzzles makes no sense. It's
too bad because Egypt is such an exciting place for a treasure hunt.