When a 32-year-old man claiming to be Stan from the future shows up in South Park, young Stan is forced to come to terms with the loser he will become. Meanwhile, South Park's own little entrepreneur, Eric Cartman, is at the helm of a new money-making venture. Cartman is in the business of revenge.
The boys, along with Craig's Gang, find some marijuana in a secluded area, left there by some older kids. They are afraid of it, but know that they must dispose of it. Stan chooses to throw the joint away saying, "It's just a stupid plant that makes you dumb, touching it won't hurt you."
That night, in the middle of a thunderstorm, an older version of Stan appears at the Marsh family's door. Somehow, apparently in the future, Stan is thrown back in time. This future Stan is in very poor condition, as apparently Stan's life has been a complete failure. He spent time in Juvenile hall, used large amounts of drugs and alcohol, and his descent all began when he first touched marijuana. He is told that the only way to save his future self is for his present self to avoid drugs and alcohol, do well in school, and stay motivated in life.
Stan, horrified of his future life, asks Butters to tutor him. While the two boys are talking, Stan discovers that Butters also has a slovenly "future self" living with him.
Stan finds the whole situation suspicious, and goes home with Butters to find his future self's wallet. In it, he finds a key card that expires in 2002. He finds the address on the back of the card, 3451 Colfax Ave, and the two boys find the building that it leads to Motivation Corp. Stan and Butters see a couple hiring an actor to pose as their son's future self, and overhear a conversation the salesman and Kevin's parents have about how it is okay to lie to kids if it keeps them away from drugs. Stan is appalled at the way parents deceive their children (in other words, the way his parents deceived him), and he and Butters decide to look in the phone book to find a place to run away to. However, they discover a "Parental Revenge Center" hotline with guaranteed results, so they decide to give it a try.
The address leads them to an office in a grungy alley, where they discover Cartman is the founder and proprietor of the business. Cartman agrees to help the two, but Stan is skeptical. Cartman's revenge plan involves going to both of the boy's houses to smear all of the walls with feces. Butters is delighted by this offer and gladly accepts it, while Stan believes that it won't solve his problem. Stan refuses the offer and decides to worm the truth out of his parents himself.
Stan repeatedly attempts to get the truth out of his parents but fails every time with increasingly blatant lies from his parents. As an example, Stan went as far as to cut off his hand with a meat cleaver to determine whether the other man is his future self - this might have convinced Sharon to come clean had Randy not been there to stop her, as he cuts off the actor's hand after distracting Stan. Stan then reveals it was a fake hand he cut off, prompting Randy to try and convince Stan it was fake in the future too, even though it is obviously a real hand. Meanwhile the Parental Revenge Agency does its job. After Cartman and a group of Hispanics smear feces all over the living room of the Stotch Household, Chris and Linda finally tell the truth about his "future self" and apologize to Butters - surprising, considering under normal circumstances he would be grounded. Randy and Sharon Marsh arrive and continue blatantly lying to Stan, insisting that more future selves must be coming back in time to the present, until Stan finally snaps and tells them he knew all about Motivation Corp. and was trying to get them to admit they lied to him. Randy finally apologizes to Stan and gives him the whole truth about drug abuse, saying that it may not kill him or fund terrorism but instead may ruin his future. Stan adds he really wishes he told him that in the first place instead of lying to him. The Stotches and Marshes then all agree what Motivation Corp. does is wrong, and hires Cartman to smear their walls with feces in exchange for freshly baked cookies.
Cartman learns that the whole experience has taught him that he should think about the future and start taking better care of himself. Moments later, a thin and handsome man, claiming to be Cartman's future self, shows up and tells Cartman that this was the turning point in his life. From this day forward, he turns his life around, and will become the famous CEO of a time-traveling company. Cartman is not convinced, believing it to be yet another Motivation Corp. actor and changes his mind, vowing to redouble his slovenly ways. Unfortunately, the man actually is Cartman's future self and subsequently changes into an obese, slovenly, obscure mechanic. Future Cartman then responds "Oh goddamn it!"