Kids of all ages, both sexes, and all reading abilities have gotten caught up in the mystery of the 39 Clues books. One thing that makes them so appealing is that they are not only books, but an exciting multimedia experience including an online game.

The final book has been anticipated practically since the series began with Rick Riordan’s The 39 Clues Book 1:The Maze of Bones almost exactly 2 years ago.

The series was mapped out by Riordan and has been written by some of the best authors in children’s literature.

The final book, Into the Gauntlet, releases today.

We are proud to wrap up the 39 Clues 39 Day blog tour with an exclusive guest post from the author of the much-awaited series finale, Margaret Peterson Haddix (one of my daughter’s favorite authors), and a fantastic giveaway!

I’d also like to invite you to tune in on August 31 (TODAY) at 4:00pm Eastern for a webcast with all 7 authors from the 39 Clues series. Find out all the details here.

******
It’s been a wild ride.

Two kids. More than a dozen adversaries. Five continents. Ten books. Seven authors.

Thirty-nine clues.

As the author of the tenth and final book in the 39 Clues series, I’ve watched the mania over the multimedia clue hunt with an odd perspective. I felt a little bit like a runner assigned to the last leg of a relay race: Even as I was cheering on the rest of my team (“Hurray! Kids love these books! Hurray! We’re on the bestsellers list! Hurray! The other books are doing great!”) I was also thinking, “Yikes! What if I’m the one who messes everything up?” The other authors were getting to do their victory laps, and I was still standing there waiting to write.

Fortunately, panic, paranoia, and fear of failing completely and letting everyone down can be very powerful motivators.

One of the advantages of writing the last book was that, even before I started writing, I heard from kids about what mattered to them in the series. Sometimes it was a detail I wouldn’t have expected—for some reason, the colors of the book covers were really, really important to many kids. In other cases, kids asked for specific plot twists that I knew they would not want once they knew all the revelations that lay ahead.

Have I mentioned that I’m actually not very good at keeping secrets?

Faced with some sweet, innocent, enthusiastic child asking, “Can’t you just tell me a little bit about what’s going to happen next?” many times I was very tempted to spill everything. But I had promised that I wouldn’t do that–and I’d like to think that I’m better at keeping promises than the average treacherous Cahill.

I also didn’t want to ruin any surprises for any readers. Another big perk of my job was that I got to read the other books in the series before they came out. So I knew how much fun lay ahead for all those readers—fun that was best when it unspooled at a page-by-page pace, with the pace picking up with each revelation, the reader pausing only to exclaim, “WHAT? Now Amy and Dan have to deal with THAT, too?”

So, for the past year, whenever kids have asked me about the 39 Clues series, I’ve had to give evasive answers. Many, many times, I had to fall back on that classic Mom line (which my own kids hate to hear): “You’ll just have to wait and see.”

But now, Amy and Dan’s story is ending.

I know lots and lots of kids have been eagerly awaiting this day, August 31, 2010, when the tenth book in the series, Into the Gauntlet, , is released to the public. They will finally get to know everything that happens to Amy and Dan.

For me, the milestone feels a little bit different. I’ve known for months what lies in wait for Amy and Dan in the gauntlet.

But now—now I’ll get to talk about it.

******

Find out what Margaret Peterson Haddix was waiting to reveal in the final book Into the Gauntlet.

The 39 Clues are a great series of books for all sorts of readers — boys and girls, reluctant or avid — looking for action and adventure. Read my “mom’s review” of 39 Clues to see if you think it would be right for your kid (or to get a glimpse into why your kid is crazy over these books).

I’m excited that one of you will be chosen to receive a complete set of all 10 books in Hardcover, with #10 being autographed by the author Margaret Peterson Haddix (U.S. shipping addresses only).

Leave a comment if you’d like to win. We’ll announce the winner on September 13 in our book column that runs every Monday here at 5 Minutes for Mom.

Disclosure: I received a set of the 10 39 Clues books so that I could familiarize myself with the series.