Ever since he ate a zapped banana, hyperactive second-grader Clyde turns into a monkey when he gets excited, so his twin sister Claudia plans to take her "monkey" to the school pet show, but when all the animals are pet-napped Clyde has to use his inner monkey to rescue them.
An unusual monkey, teased because of his colorful markings, keeps to himself from summer through fall, but when the younger monkeys become bored in the winter, they begin to appreciate Cyril's differences.