Will Allen and the Great Monster Detective (The Chronicles of the Monster Detective Agency) by Jason Edwards

Description

Will Allen may be one of the smallest boys at Ashford Middle School, but he is also one of the smartest. But cleverness alone isn't enough to help him when monsters infest his room!
Together with his friend Jeannine Fitsimmons, Will searches fruitlessly for help, until a strange business card appears, instructing them how to summon Bigelow Hawkins, the Great Monster Detective. With Bigelow's help, along with the use of his very special monster-fighting instruments, the RevealeR and the MonsterScope, Will must learn how to conquer his monsters and reveal the secret of the dreaded HIDDEN BEAST before it's too late…