Stan and Cartman are in a speedboat that Cartman claims is owned by his Uncle Roy. Stan is behind the wheel of the boat and after Cartman says he will take full responsibility for whatever happens to the boat they get the boat started and go wildly careening about out of control. The boat crashes into a large beaver dam. The boys manage to escape unharmed, but the both the boat and dam are damaged beyond repair. The dam was poised over the town of Beaverton, Colorado, which now finds itself underwater. The news reports speculate as to what is going on in Beaverton, but no one is actually doing anything to help the victims. Meanwhile the residents of South Park speculate as to who is at fault for the collapse of the dam (George Bush, terrorists with their beaver dam WMDs, FEMA or the mayor of Beaverton). Stan knows who is really to blame and feels guilty that no one is helping anyone in Beaverton. His dad tells him that isn't as important as figuring out who is to blame. Cartman doesn't want Stan to tell Kyle anything about what they did. The cause of the flood is revealed as "Global Warming." Randy Marsh warns a committee that a global warming catastrophe the likes of which no one has ever seen before will occur the "day after tomorrow." Scientists break into the meeting revealing that the events will start to occur "Two Days Before the Day After Tomorrow," which means today. Mass panic breaks out. When they can't evacuate the Marsh family and others find themselves holed up in the Park County Community Center.
Stan is still worried about the people in Beaverton. The news exaggerates the affects of "Global Warming." Stan admits to Kyle about what really caused the Beaverton flood. To atone for his behavior Stan decides to go and help rescue the people in Beaverton. Randy Marsh tells everyone that they can't leave the community center, because the effects of "Global Warming" are going to cause the outside temperature to drop to "70 million degrees below zero." Stan, Kyle and Cartman have another boat that they are trying to pilot in an attempt to rescue the folks in Beaverton, but with this boat they crash into an oil refinery, which results in them setting the floodwaters on fire. Stan calls his father for help and Randy, Gerald and a guy named Steven put on every warm piece of clothing they can find and attempt to hike to Beaverton. The Army is finally mobilizing their forces for rescue efforts and scientists have determined that "Global Warming" wasn't too blame for the Beaverton flood.
The boys are still trapped in the refinery and Army helicopters are finally flying overhead in Beaverton. The boys try to get to the roof, but before Cartman will let Kyle get up to the roof, he demands that Kyle hand over his "Jew gold." Kyle relents and boys make it to safety. They are returned to South Park and they learn the "Global Warming" wasn't to blame; it was the "Crab People." Stan admits to everyone that he broke the dam, but his confession is misinterpreted and soon everyone is admitting to breaking the dam.