After being turned down for a Credit Card by the Camden Savings & Loan because he doesn't have a job, education or a permanent place of abode, Earl's feeling down. It's the realisation that he's never become an adult.
All he's got is the list, but Joy points out even that's not spelled correctly and he doesn't follow the numerical order, so Catalina suggests he puts himself on the list seeing as he fiddled himself out of growing up, so Earl enters the world of subsets: Number 273 - Kept Myself from Being an Adult; 273a - Finish High School; 273b - Get a Real Job; 273c - Move Out of the Motel.
Having flunked out of school, passing his General Education Development certificate proves harder than Earl imagined, so he heads back to High School to convince his former teachers to help him pass the tests. However the teachers remember him too well, and after years of being abused by Earl and by all the apprentice Earls who have passed through their care since, they're unwilling to help... unless Earl does something for them first.
After an arrangement that starts with Earl taking on the worst class and ends in an exploding 1968 cobalt blue Camero, the teachers get revenge on the kids and regain some self-respect, and Earl gets a hand in getting a third of the way to becoming an adult as he passes his G.E.D.