Bruce is frightened of becoming a butterfly because he's terrified of heights. Worse yet, the other caterpillars tease and bully him. Unwilling to suffer any more, Bruce runs away from home. Along the road, Bruce makes some unlikely friends, including a young moth caterpillar. Smitten by her, Bruce is horrified when she is captured by a bat while he hides. Angered by his cowardice, Bruce resolves to rescue her, and his other friends--a mockingbird who doesn't eat bugs because she is a vegetarian, a spider who got tangled in his own web, and an aging firefly--join the search. When they reach the bats' cave, however, hope of a rescue vanishes when they are captured by the bats' evil leader, Stang. Bruce learns that Stang and his minions have brutalized or killed many, including other bats, during his rise to power. Bruce's unwillingness to cower any longer helps him devise a plan to save all the captives and end Stang's ruthless rule: Bruce must convince the other bats to join him.