30 books • 7 series
The Lost Ninja
Book #4: Your Very Own Robot (Choose Your Own Adventure - Dragonlark)
Book #6: House of Danger
Book #16: Secret of the Ninja
Book #36: Owl Tree
Book #48: Spy for George Washington
Book #57: The Antimatter Formula
Book #66: Secret of the Ninja
Book #73: Beyond the Great Wall
Book #92: Return of the Ninja
Book #8: El secreto de los ninja / Secret of the Ninja