Summer arrives and the school bell rings but Mr. Garrison won't let anyone leave until Mr. Hat is returned to him. The instant he turns his back, everyone leaves, excluding Pip, who has to stay for summer school anyway. The snow has melted and Stan, Kyle, Cartman, and Kenny go to buy fireworks for the 4th of July, but soon discover that all fireworks have been banned in the state of Colorado. The ban was enacted after a kid from North Park blew his hand off with one. The only thing that wasn't banned was black snakes, but the boys don't buy them because they find them to be incredibly lame. Cartman leaves the guys to go to his swimming lesson, but Stan and Kyle warn him that the first Graders urinate in the pool.
Upon finding out about the recent fireworks-ban, Jimbo and Ned decide to help the boys by smuggling in some fireworks from Mexico. Unfortunately, when crossing back into the American border and being asked questions by the border patrol; Jimbo forgets to reply "no" to the question "do you have any firearms or explosives in the vehicle?" Both he and Ned are arrested for attempting to smuggle fireworks into the United States.
Mayor McDaniels has already heard about the firework ban and tries to come up with a way to make the 4th of July Celebrations worthwhile despite that. She gets people to come up with something, and they soon realize that even though black snakes are still legal because of their harmlessness, there was no law stating how big a black snake could be. They informed the mayor that their idea was to make the world's biggest black snake. It will be put in a huge dish surrounded by flamethrowers. When they leave, it is shown that Mayor McDaniels is sitting in her office letting Officer Barbrady perform oral sex on her.
At the celebration, the snake is lit but it begins to grow out of control and starts destroying the town.
Meanwhile, Mr. Garrison has gone to a psychiatrist, Dr. Katz, who explains to him that his puppet, Mr. Hat, is what he uses to express his repressed homosexual feelings. The giant snake smashes through the window and kills Dr. Katz. At a sauna, Brett Favre meets Mr. Hat, who moves his eyes proving he is possibly sentient.
The boys phone Chef about the problem with the snake. But he is on a holiday and tells them to "fudge themselves". Jimbo and Ned arrive with fireworks. As the fireworks are set off, they impale the snake, destroying it, and causing it to rain black ash over the town.
At the swimming pool, Cartman finally swims to the deep end, but as the pool reopens the first Graders urinate right in front of him.
Instead of the snow, the boys use the ash from the snake to play with, as does everyone else. Mr. Garrison walks by and introduces Mr. Hat's replacement; Mr. Twig. Chef arrives back and sees everyone is covered in black soot from the ash and assuming they are dressing in "blackface", he tells them to form a line so he can "whoop their asses".