It's the beginning of summer vacation, but, alas, naughty Zip and Zap are shipped off to the strict Hope Re-education Centre for summer school! Headmaster Falconetti is a no-nonsense disciplinarian, intent on transforming the unruly summer students into productive members of society, and he seems especially keen to make an example of the mischievous twins. Sick of being disciplined, the brothers and their sidekicks Filo and Micro decide to band together and have a little fun. Dubbing themselves "The Marble Gang," they bravely defy all the rules, but only under the cover of night, which gains them a hushed admiration from their classmates, including the headmaster's visiting niece Matilde.