Kenny excels at playing the game Magic: The Gathering. He has the boys’ full attention until a new, hard-core activity gets in the way. When Wendy tries to get Stan to pay attention to what she’s doing, she realizes that what he does with his guy friends always comes first.
The episode begins at South Park Elementary, where some of the girls on the Volleyball team are handing out fliers for the game. However, all of the boys are too busy because of the upcoming fight between Kenny and a person named Slaughterhouse.
It turns out that Kenny and Slaughterhouse are simply playing Magic: The Gathering. The boys and other South Park townsfolk watch in suspense as Slaughterhouse is picking his card. When he finally does, he is expertly defeated by Kenny.
The next day, the boys are still discussing the previous night's "fight", citing it's carnage and ruthlessness. Wendy Testaburger walks by and is asked by Stan Marsh if she had heard about "last night". She begins to talk about the Volleyball game and is quickly dismissed by Stan. The school janitor overhears the boys and entices them with "real man shit" and gives them an address.
That night, the boys find that the "hardcore shit" is at City Wok. Tuong Lu Kim makes them pay five dollars to get in. They go down to the basement and find many people betting on Cock Magic.
Cock Magic is when roosters play Magic: The Gathering.
The next day, at McDonald's, Kenny displays doubts about the roosters' happiness and the others decide to buy a rooster and train him with Kenny's Magic: The Gathering skills.
The boys are being lectured by Randy Marsh, who believes Cock Magic is when you perform tricks with your penis.
The boys go to a poultry dealer, and select a young chicken and name him "McNuggets".
Randy is practicing his Cock Magic in the bathroom and Sharon Marsh catches him. However, he talks her out of it.
At the City Wok, McNuggets fights another rooster and wins. A business man gives them an address to the "big leagues".
The next day, Randy performs Cock Magic at a kindergartner's birthday party, successfully scaring the children.
At South Park Elementary, the boys talk about McNuggets' win. The coach of the girls' volleyball team talks about the turnout and tries to get people interested. Stan makes a rather funny joke about the volleyball team only to find out Wendy is the captain of the team.
Sergeant Yates investigates Randy's Cock Magic, misunderstanding the tricks as the underground rooster fights. Yates arrests the woman who called the police initially.
That night, the boys, except for Stan, go to Panda Express for Cock Magic. The owner makes them pay ten dollars to get in. The boys are intimidated by a rooster named Gadnuk, Breaker of Worlds. Stan is at the volleyball game, although he is on the phone with Eric Cartman who tells him about the game. Kenny takes the place of McNuggets in the fight against Gadnuk. Kenny almost beats him when the cops bust in and tell everyone to freeze. When asked how they were found, Yates tells them that there were fliers. However, no one put out fliers. Suddenly, Randy is on stage and he performs his cock magic. This distracts the cops and all the people who were involved in the cock magic fights use this chance to escape.
The next day, the boys again discuss the previous night's events. Stan decides to help the girls' volleyball team and the episode ends with the South Park team playing against McNuggets in a hybrid of volleyball and Magic: The Gathering.
AV Club gave "Cock Magic" a "A-" rating saying: "To be fair, two of “Cock Magic”’s three storytelling pillars—cockfighting, Magic: The Gathering, and, um, penis magic shows—actually do pop up quite a bit in the news. But the stories have been the same for years. Most people agree that forcing roosters to fight each other to the death is wrong, and folks have been arrested for it as recently as last week. Players of Magic tend to get obsessive about the game, resulting in a strict limit on the number of tournament contestants as recently as yesterday." 
IGN gave "Cock Magic" a "6.5" rating, saying: "Sometimes you can sort of tell when Matt and Trey are struggling to come up with an idea for a new South Park episode, and this week's "Cock Magic" definitely felt like an eleventh-hour mashup. Clumsily combining Magic: The Gathering with cockfighting, tonight's episode was lacking in solid storylines and consistent humor -- but I guess it could have been worse."