What came before The 39 Clues?  Spy X, of course!  I think my interest in espionage began when I accompanied the First Lady to Moscow (along with R. L. Stine and Marc Brown) for the first Russian Book Festival.  I loved traveling in motorcades, surrounded by Secret Service and military.  I thought: Hmm, a government career? … what would be cooler than being a spy?  Then my editor friend Kendra Levin gave me an idea for a spy series, and in the interest of personal safety, I decided to write that instead.

Spy X begins on a special day for Andrew and Evie: their 11th birthday, on the 11th day of the 11th month.  But that morning at breakfast, all they find is a hasty good-bye note.  It’s from Mom, who is a government worker in covert operations.  She’s gone underground — for a long, long time. 

But there’s something about the note … and the unmarked boxes that start appearing at their door … and the lady dressed in purple next door.…  Soon Andrew and Evie are in a race to find their own mother — against an enemy they don’t know, in a world where no one can be trusted.

Although the Spy X series sold nearly a million copies, sadly, it’s now largely out of print.  But Book #1 is still available from most booksellers, and books #2–4 can be ordered from second-hand sellers.