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SAN ANTONIO — As the Cahill clan gathers near Boston for matriarch Grace Cahill's funeral, a select group of family members are summoned to the mansion's great hall and issued a challenge by the executor of the estate.

"If you so choose, each of you may walk out of this room with one million dollars and never have to think of Grace Cahill or her last wishes again," says Mr. McIntyre, the seemingly guileless attorney. "Or ... you may choose a clue — a single clue that will be your only inheritance. No money. No property.

"Just a clue that might lead you to the most important treasure in the world and make you powerful beyond belief ... or it might kill you. One million dollars or the clue. You have five minutes to decide."

As the buzzmakers surrounding this much-anticipated new adventure series are fond of asking, "What would you do?"

"The 39 Clues," an innovative "multiplatform" entertainment combining books, card collecting and online gaming for kids ages 8 to 12, officially llaunched Sept. 9.

San Antonio writer Rick Riordan, the 44-year-old creator of the best-selling "Percy Jackson and the Olympians" series for young adults, was hand-picked by Scholastic, the publishing giant that brought us "Harry Potter," to write the first book in the series, "The Maze of Bones."

"We drew up our dream list of authors, and Rick was No. 1 with a bullet," says David Levithan, executive editorial director for Scholastic and the guiding force behind "The 39 Clues."

"We're all huge fans of Rick's 'Percy Jackson' books. The way he combines action and adventure with humor and history was exactly what we wanted. And when we sat down with him and told him about the concept, he got it in the first five sentences."

The former private school teacher, who also created the Edgar Award-winning Tres Navarre mysteries set in the Alamo City, envisioned the arc of the story line over nine more volumes.

Each leads readers/players closer to clues "spread across the world in the darkest, most dangerous places," says Riordan — and possibly to real-life treasure, actual prizes valued at more than $100,000.

And each installment deals with a different historical epoch, embodied by a well-known historical figure.

"It's sort of greatest hits of history," says Riordan.

In "The Maze of Bones," for example, unraveling the central clue requires fairly in-depth knowledge of Benjamin Franklin. Riordan's own research of Franklin led him to some fascinating facts, he said.

"One of the interesting things I found was that he enjoyed working magic number puzzles," Riordan said. "He would be sitting in these meetings, bored, so he came up with these puzzles, which were basically Sudoku, except he was doing it 200 years earlier."

Because he was a middle-school teacher for more than 15 years, Riordan understands the difficulties of pulling history off the page and making it interesting to kids.

"When kids read a book they want to imagine themselves into the story," Riordan said.

At "The 39 Clues" Web site, Riordan expands on this notion in a video: "When I was a kid, I spent of lot of time imagining I was related to somebody famous. I used to think it would be so cool to be the great-great-great-grandson of Mozart ... Or maybe I could be the descendent of Amelia Earhart and be a great explorer."

As Riordan explains, Cahill blood flows through the veins of virtually every important historical figure of the past 500 years. And, after a quick read of an advance copy of "The Maze of Bones," that list also includes Benjamin Franklin, Lewis and Clark, Abraham Lincoln, Eleanor Roosevelt ... even Harry Houdini.

"The 39 Clues" combines 10 books, online gaming and card collecting. Kids can glean clues to the treasure from the books and cards, then log on and play the game themselves on the Internet. One lucky winner will walk away with a grand prize of $10,000 cash.

"The neat thing is they can get online and actively become a Cahill and search in real time for clues," Riordan says. "The hope is to get a lot of kids reading who are not necessarily bookies, but might be more into cards or gaming — like my kids."

Riordan, who admits to being a Dungeons & Dragons "total geek" in high school circa early '80s, plays online games with his sons.

As with the "Percy Jackson" series, "The 39 Clues" has been a Riordan family project. Sons Patrick and Haley got first peek at the manuscript and made a good sounding board for the adventure.

"I write with my sons in mind," Riordan said. "This one was an enthusiastic thumbs-up."