You will be able to get a very detailed account of the plot with the link below, but I will give a broad overview.
The Vigils is a school gang headed by Archie Costello. They give various assignments to students in order to cause trouble for them. A student known as The Goober is given the task of sneaking into a classroom to unscrew desks, chairs, and hinges, loosening each part. When everything falls apart the next day, The Goober is never quite the same again.
The Goober's friend, Jerry Renault, is soon given the assignment of refusing to sell chocolates at the annual chocolate sale. Jerry is then supposed to agree to sell chocolates after ten days. It becomes common knowledge Jerry is just doing this because of the Vigils, so no one is really upset about it.
After the tenth day, Jerry still refuses to sell chocolates, however. He has decided to rebel against The Vigils and the whole chocolate sale because a poster in his locker inspires him to continue his boycott of the chocolate sale. The poster says, "Do I dare disturb the universe?". Jerry decides he will disturb it.
The Vigils are upset that Jerry is defying them, but Jerry becomes a hero in the school, and chocolate sales plummet. Brother Leon accuses Archie and The Vigils of ruining the sale, so Archie comes up with a plan to make Jerry look bad. The chocolates start selling again because The Vigils are selling all of them and making it look like the other students are doing it. The Vigils constantly harass Jerry. They steal his homework and trash his locker and even have some guys beat him up.
Then Archie decides to get back at Jerry by setting up a fight against Emile Janza, a thug. Jerry gets in one good punch, and Emile decides to get rid of the rules. Jerry collapses after being punched over and over. Another teacher finally stops the fight. Brother Leon, however, was watching Jerry get beat up the whole time and keeps Archie from being punished.
Jerry tells his friend, The Goober, not to disturb the universe because it isn't worth it. Jerry has a broken jaw and some internal injuries. Archie gets away with everything and isn't sorry for what happened to Jerry, who loses hope for the future.