Jack Rankin's not happy with his dad, John, the school janitor. This is because John has committed the cardinal sin of embarrassing his son in front of other students. He didn't mean to, of course, but Jack's pretty embarrassed all the same.
When John walks out the classroom door after clearing up someone's sick, he says "Hi, son" to Jack. Jack mumbles "Hi" in return, but it's pretty obvious that he's really embarrassed. Although he loves his dad and is proud of the work that he does, Jack knows that some of the other students will give him hell about John's being a janitor. And sure enough, they do. No sooner has John left the classroom than a boy called Kirk Dorfman starts picking on his son.
Jack is pretty annoyed at this and resolves to get even with the rich kids who give him grief about his dad. But in actual fact, he takes out his anger and frustration on John. He does this by vandalizing a desk with some Bubblicious watermelon gum, which is sticky as well as stinky, the ideal gum for the job.
Unfortunately for Jack, Mr. Ackerby, the school principal, works out that he was responsible for vandalizing the desk and so hands down a punishment. Every night after school for the next three weeks, Jack will be on gum cleanup duty for the chief custodian. Unbeknownst to Mr. Ackerby, the chief custodian just happens to be Jack's father.