‘Potter’ publisher looks to promote next big thing

On Sept. 9, the U.S. publisher of “Harry Potter” will premiere a highly ambitious series with a mystery ending for readers and a couple of puzzlers for the industry: How big is the market for a multimedia story — and can a phenomenon be conceived by a publisher rather than created by the public? “The 39 Clues” is a planned 10-volume set about young Amy and Dan Cahill and their worldwide search for the secret to their family’s power. The first book, “The Maze of Bones,” is written by Rick Riordan of “The Lightning Thief” fame and has an announced first printing of 500,000. Steven Spielberg has already acquired film rights to the series.