You need the blueprint from Nate's locker to end the passageway in the detention room. Assemble the comic strip pieces and show them to the guy at the comic shop, and get some gum. The locker combination is written on the strip. You also need to make a stink bomb in the science room (yellow + blue + heat) to get rid of the teacher once you go to detention.
It it in the secret passage in the detention room on Big Nate Island.
You have to get in detension
in the detention room
get the bell clapper
in the cabinet on big Nate island
In Nate's locker. The combination is on the assembled comic strip.
It is in the secret store room behind the filing cabinet in the detention room on Big Nate Island. You need the blue prints from Nate's locker in order to access the secret room.
you climb up the rope
The clapper.
you use the stink bomb wow
Go to the right and click on the file cabinet cuz its a secret passage way and thats where you find the bell clapper
You are only in detention to get into the filing cabinet, which has a secret passage behind it. Before chewing gum to get detention, there are two things you need : a stink bomb and the blueprint from Nate's locker. (see related question)