In Nate's locker. The combination is on the assembled comic strip.
On 24 Carrot Island, the vent diagram is in a window near the roof. On Big Nate Island, the school blueprint is in Nate's locker. The secret map to the Time Capsule is under a rock on Seal-Saw Island.
in the cabinet on big Nate island
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.
It it in the secret passage in the detention room on Big Nate Island.
You have to get in detension
you use the stink bomb wow
in the detention room
get the bell clapper
pull the power switch on
In the file cabinet, in detention, in the school.