Flatulent Canadian superstars Terrance and Phillip have broken up over creative differences. When the boys discover their idols have called it quits, they'll go to any lengths to reunite the duo and recruit them for South Park's Earth Day festivities.
While the boys are watching a rerun of Terrance and Phillip, a commercial airs for Terrance and Phillip: Live at the Denver Coliseum Thursday night. They are hysterical, and are determined to see the show. At school the next morning, Kyle tells the other three he got them all tickets. Ms. Choksondik announces that Earth Day is coming up on Friday and that the national Earth Day organization has chosen South Park to be the location of the Earth Day Brainwashing Festival. Three environmentalists speak to the class, using Jedi mind tricks to force their message upon the children ("You care very much about the earth, don't you?", "we must save the earth from Republicans" and other such propaganda). The boys, however, anger them, claiming they can't help set up for the festival since they'll be seeing Terrance and Phillip. When this fails to sway the environmentalists, Kyle claims that they will be there to get Terrance and Phillip to perform at the festival. The environmentalists agree to let them go, but warn Kyle that he had better not promise things to the Earth Day people that he cannot deliver.
At the show, the boys discover that Terrance has gained a considerable amount of weight and is now performing with a Phillip stand-in who neither looks nor sounds like the real Phillip. Determined to find out what's going on, the boys visit Terrance in his dressing room by sneaking through in the pants of an extremely obese groupie. Once inside, the boys ask Terrance about performing at the Earth Day festival and about Phillip's absence. Terrance grows upset at the mentioning of Phillip, and explains to the boys that he and Phillip have gone their separate ways, with Phillip performing Canadian Shakespeare in Toronto. Back in South Park, the boys tell the environmentalists that Terrance and Phillip have parted ways. The environmentalists become violently angry, as they have already heavily promoted the appearance. The boys are told to go to Canada immediately to convince Phillip to perform, or else. After sitting through a Canadian performance of Hamlet, the boys confront Phillip and ask him if he will appear at the Earth Day festival. Phillip is receptive until Kyle mentions performing with Terrance, which Phillip flatly refuses to do. Kyle again lies and says that the people of South Park only want to see Phillip anyway, not Terrance. Phillip rejuvenates his interest, agreeing to come, but all four boys worry about what will happen when Phillip finds out that Terrance is at the festival too.
At the festival, the boys assure the environmentalists that Terrance and Phillip will both be there any minute. Determined to keep up the pressure on the boys, the environmentalists use a meat cleaver to chop off Kenny's left arm. Kenny screams and cries as blood slowly pours out. A moment later Phillip shows up, followed quickly by Terrance. The two are initially furious to see one another, but they reluctantly agree to work together. During their rehearsal, Terrance and Phillip begrudgingly do a routine, which eventually boils down into an argument until they both leave in a huff. The boys are dismayed by this, but not nearly as much as the environmentalists, who tell the boys that they had better get Terrance and Phillip back together before the show starts, or else. For good measure, the environmentalists chop off Kenny's right arm and Kenny shouts out more in pain. When the show finally starts and Terrance and Phillip are introduced, Kyle instead hastily puts on a video of the documentary Terrance and Phillip: Behind the Blow. Though the crowd seems pleased by this, the environmentalists become furious and chase the boys. While the chase is in progress, Terrance and Phillip both notice the film that is playing, and both stop to watch the story of their career.
As the boys are being chased, the environmentalists soon chop off Kenny's left leg and Kenny bleeds furthermore as he's hopping on his remaining foot to catch up to the boys. Back at the festival, Terrance and Phillip eventually happen upon one another in the crowd and, after seeing what an incredible career they've had together, exchange apologies and decide to perform for the crowd. At this point, the boys and the environmentalists both arrive back at the festival, where the environmentalists chop off Kenny's right leg. Kenny falls limbless and quickly bleeds. Just as the environmentalists move in to finish off the other boys, Terrance and Phillip take the stage and begin performing their routine. This thrills everyone - even Kenny, who is somehow still alive.