The Diary of a Secret School Spy.

This story stars a common sixth-grader, Mile Anderson who enters a mysterious dimension filled with spies, secrets, robbers, secret agents, and more! How will Mile manage in this CRAZY dimension? Every kid in the universe will enter this dimension someday or the other. Maybe you have already entered it and you know it. The dimension is:

MIDDLE SCHOOL

I would personally suggest this book for children aged from 8-12. This book is specially for those children who are really into spies and thriller books like Nancy Drew books