Cartman is imagining he is in Mars as the episode starts, he is floating around as various places are shown including a amusement park on the planet. The camera then shows Heidi, who is sitting down with him as they eat. Cartman snaps out of his daydream and talks about Kyle changing, telling Heidi that he is worried that they are "losing Kyle".
Gerald is on his computer trolling as his doorbell rings. He opens it to find his fellow trolls standing there. Inside, the trolls are drinking beer celebrating as Gerald is panicked. Gerald tells Dick that he wants to talk to him in private. In the kitchen, Gerald tells Dick he wants no part of this. Dick tells him they could have a big impact on the election. But Gerald tells him he does not want to troll to be political.
At the Marsh Residence, Garrison and Randy are in the kitchen. A member berry is held down by a paperweight. As it "members" various things, Randy takes a torch to it. It screams and then instantly turns back to normal, Randy tries again this time using acid, it screams again and once again turns back to normal.
At the Broflovski Residence, Kyle is in the bathroom on the toilet as Cartman barges in. Cartman and Heidi both walk inside of the bathroom as Kyle panics and covers his genitals. Cartman tells him that once you have a girlfriend, you stop caring about seeing each other in the bathroom. Kyle angrily says he is going to the bathroom. Cartman starts to talk about how Kyle has changed and how he would find Skankhunt42. He asks Kyle why he has changed as he sprays Kyle with air freshener. Cartman tells him that Heidi has found a way to identify the troll.
Gerald is on his computer, still trolling people, before then, Dick requests to FaceTime with him. He starts to sing to Gerald, who hangs up on him and continues to troll.
In Heidi’s house, Eric, Heidi, and Kyle enter Heidi's room. Kyle looks shocked as a wall is shown with pictures of almost every student and adult at South Park Elementary. Heidi says she analyzes emoji patterns and the troll’s writing to determine who the troll is. It is revealed that the troll is a adult and a parent. Kyle says Heidi’s idea of “Emoji Analysis” is genius while, Cartman tells him he didn’t give her credit for also being hilarious.
In Denmark, Freja Ollegard’s memorial is shown as various people walk around town. The Troll Trace building is shown. Inside, one of the employees tells Lennart that they used Emoji Analysis and found out the troll is in Colorado.
Back at the Marsh residence, Randy is electrocuting a Member Berry when he gives up. He says they can’t be killed as Garrison notices the jar is empty. Randy tells Garrison that he must speak to the American people. Garrison doesn’t want to give a speech, but Randy is able to convince him that if he doesn't want to win, he will have to do so.
At the Broflovski residence, Kyle is doing homework as Cartman comes into his room. Cartman tells Kyle that him not telling Heidi she was funny wasn't cool. Cartman accuses Kyle of having a hang up with woman. Kyle goes over to Cartman and tells him that Trolltrace.com can track anybody’s internet history.
Cartman says he isn’t worried because they don’t use the internet. Kyle says he’ll print out his internet history and give it to her. Cartman panics as a flashback starts, rewinding the entire season. It stops at the movie theater, where Cartman walks out after seeing the Ghostbusters movie with his mother. He texts Butters telling him that chicks ruined the movie and he shouldn't bother going to see it. The flashback goes back to the present moment as Cartman panics about his internet history being public.
Meanwhile, the member berries have escaped the jar and are leaving the house.
At the Broflovski residence, Dick knocks on the door with a gift in his hand. He tells Gerald he wants to be friends with him again. He and Gerald start to get into an argument as Gerald tells him that he doesn't troll to make a political change but to laugh at the misery of his victims and remember when he used to bully as a kid and he proves it with a trolled picture of Sheila. Dick becomes shocked to realize Gerald is just a sadistic asshole instead of the ultimate rebel he thought he was. Gerald replies that Dick isn't a political activist either, but a small giant that is lashing out at everyone because he can't get a relationship. Dick then decides to cut relations and lectures him on provoking people for no reason, but Gerald tells him to stop trolling him and shuts the door.
Back in Denmark at the Trolltrace.com building, they track the town of Fort Collins as a location for internet troll MLKKK. The town of Fort Collins is shown peacefully as the camera zooms into a house. MLKKK is on his computer as a alarm and sirens go off. He turns on the TV and the news reporter says everybody’s internet history in Fort Collins was made public. People run out in the streets. MLKKK’s phone rings, and an angry man says he knows where he lives. MLKKK runs off and gets into his car. He quickly gets into an accident as the town of Fort Collins is in a state of panic. Fires are started, cars crash, and marriages are destroyed.
The woman in the other car involved in the accident runs up to MLKKK and grabs him, freaking out about her internet history being public. MLKKK runs off and an angry man along with his disabled daughter in a wheelchair stop him. The man throws gasoline on MLKKK and lights him on fire.
On a highway, cars are driving by. A small white RC-style car appears with the member berries driving it. They member various things before pulling over and going to the trunk. A bloody member berry is inside with it’s mouth shut. “We’re gonna kill you, member”, they say before closing the trunk. They return to the small car and drive off, membering things.
Breaking News appears as the news anchor reports on the events in Fort Collins. Fort Collins is shown with a massive car pileup and fire at a 4 way intersection. Gerald watches in shock, and MLKKK is shown burned alive. He FaceTimes Dick who ends the call after Gerald tells him the Danish got into people’s internet history.
Cartman is on Mars again, and a storm is happening as Cartman’s dream falls apart. The camera fades out to Heidi who asks if Cartman is okay. Cartman says he’s going to be honest with her and starts lying saying that at the Ghostbusters movie, Jimmy took his phone.
He freaks out, worried that people will see the bad things he’s done online. Heidi thanks him for being honest and they hold hands as Cartman floats around on Mars. Heidi says emoji analysis will determine where any comments come from. Cartman is now in a heavy wind storm in Mars, and he gets sucked away.
Garrison addresses the nation, saying that America must face the fact that the new Star Wars movie was not good and that a vote for Clinton reminds the world that America thought the new Star Wars was like a Happy Days reunion special.
Hillary’s advisers walk in saying that TrollTrace.com must be stopped, and they hand her a folder with SkankHunt42 on it.
The member berries push the captured member berry into a martini glass. It is served to Caitlyn Jenner, and as the server asks her about this year's election, she replies with her catchphrase “Buckle up, buckaroos” as the episode ends.
AV Club gave "Fort Collins" a "B+" rating saying: "It doesn’t pack a ton of urgency. Heidi’s Emoji analysis suffers the same fate, adding up to little more than a lot of talky detective work. Even as Trey Parker and Matt Stone make observations about the dangers of online policing, there’s still a sense of the episode searching for something. Maybe they’ve already figured out how this all ends, or maybe they haven’t. Either way, everything comes off as a bit scattered right now.
But as they’ve done with many plot-heavy episodes in the past (as recently as last season), the creators upgrade “Fort Collins” from a mediocre half-hour of South Park to a slightly above-average one by using their greatest weapon: jokes. Even as the story wanders, the gags work independently of the unfocused plotting"
IGN gave "Fort Collins" a "9.2/Editors Choice" rating saying: "South Park's 20th Season keeps getting weirder and more entertaining with every new episode. This week added new drama to the growing Denmark conflict and finally brought Cartman back into the spotlight. But none of the show's regular cast could compete with the Member Berries, who are now emerging as some of the best South Park villains in recent memory."