Milo and Zack go on a quest to help Melissa get a book she left behind at school.
Milo, Zack, and Melissa return to Jefferson County Middle School after school hours due to Melissa forgetting her math book in one of the classrooms. As they head in hoping to find it, Melissa and Milo discuss the existence of the "Great key-keeper" aka Fred the janitor, who supposedly sends students on "quests towards enlightenment." After obtaining a key to the classroom from Principal Milder, the trio recover the book only to forget the key inside the room, which locks behind them. Despite Zack's disbelief, Milo and Melissa then believe that Fred is providing signs that will help them find him so that they can get back into the classroom and recover the key.
The trio's "quest" takes them into the janitorial office - where they encounter Mr. Drako - and then into a locked storeroom that opens up into the old school library. They then discover a secret passage that leads to their science classroom, and eventually make their way outside where Coach Mitchell informs them that he saw someone on the roof. Investigating they fail to locate Fred, but do discover a roof hatch that enables them to get back into the class and recover the key, which they then return to Principal Milder. Fred then appears to Milo and Melissa and asks for their help in cleaning up the mess caused by their "quest."
The image gallery for The Math Book may be viewed here.
The segment was first released on the Disney XD app prior to its premiere date.