A substitute teacher means only one thing—it's time to play some tricks!

Brother Bear is just starting to get nervous about tomorrow's big history test when Teacher Bob announces that the students will have a substitute teacher for the next three days. According to mischievous Too-Tall Grizzly, there's only one way to deal with a grouch-puss old sub: pranks!

Instead of studying, Too-Tall, Brother Bear, and Cousin Freddy stay up all night coming up with wacky jokes. They get a trick book and some fake spiders—they even put a frog in the teacher's desk! But when the sub turns out to be more fun than they imagined, the boys realize they may have made a terrible mistake. Will they have time to undo the jokes before the test? Or are they about to become history?