Starred Review. Built around a ripe conceit?wealthy matriarch scatters cryptic clues to a mysterious fortune around the globe?this first installment in a projected 10-book series is tons of fun. Lead-off hitter Riordan (The Lightning Thief) mixes just the right proportions of suspense, peril and puzzles in a fast-paced read (Riordan mapped the narrative arc for all 10 volumes, but other high-profile authors will be writing for the series, too). Likable orphans Amy and Dan Cahill have moxie (plus Dan can memorize numbers instantly) and frailties (Amy hates crowds). As the siblings compete with less honorable members of the Cahill clan, all distantly related to Benjamin Franklin, to win the fortune by collecting all 39 clues (only two are found in this first book), they learn about their dead parents, each other and world history. The humor is spot on?one uncle is credited with inventing the microwave burrito. The only flaw? The story does not end so much as drop off a cliff. (The second book, One False Note by Gordon Korman, is set to arrive in December.) While waiting, readers can collect cards, each of which contains evidence, and play the online game (www.the39clues.com), for which Scholastic is offering over $100,000 in prizes. This ought to have as much appeal to parents as it does to kids?it's Webkinz without the stuffed animals, and a rollicking good read. Ages 9?12.