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?