Complex sentence: In May 2009, a new "middle grade" series entitled "Untold Adventures" began with books titled "Pyramid of the Sorcerer" and "Mystery of Mount Sinai".
Split into simpler sentences: In May 2009, a new "middle grade" series entitled "Untold Adventures" will begin. The first two books are entitled "Pyramid of the Sorcerer" and "Mystery of Mount Sinai".