The race to uncovering the Cahill family mystery continues, as Scholastic Media and Post Cereals join forces on an upcoming promo for publishing property The 39 Clues for 2010.

Launching in tandem with the publication of book seven (The Viper’s Nest) in January and book 10 in August, the promo will feature the book series on more than four million branded cereal boxes for each six-to-eight week promo on Honeycomb, Alpha-Bits, Golden Crisp and Waffle Crisp brands. It’ll be supported by national print advertising along with additional branded content for a Race to Win Sweepstakes from the cereal company beginning January 5, 2010 in advance of the February publication of book seven.

Families will be able to enter for a chance to win one of four grand-prize four day/three night trips to New York City (inclusive of airfare and hotel from Funjet Vacations) and compete in a 39 Clues Scavenger Hunt for a secret bonus prize. There will also be 200 first prize 39 Clues Prize Packs which include a 39 Clues backpack and signed set of the books. Consumers can enter by decoding evidence on the back of the specially marked cereal boxes and entering a code at Post39CluesRacetoWin.com. Post will support the promo with exclusive branded games, a free screensaver and an online chance to enter the sweepstakes. In August 2010, in conjunction with the tenth and final book in the series, Post Food will run a second promo.