It's Halloween at GCC, and many students are getting sick with a mysterious illness that seems to turn them into zombies. Pierce is the first one as he bites into Star Burns's arm. Dr. Richard from Annie and Jeff's pottery class is called to help. Meanwhile, Troy asks Jeff for advice on attracting women after his staged Alien vs. Ripley battle with Abed fails to get him any phone numbers.

Troy makes himself a sexier costume to wear while everyone watches the zombie disease symptoms get worse. Star Burns tries to attack Annie and Richard. Dean Pelton calls the army surplus store where he got the party's taco meat, thinking that's what's poisoning the students, but it turns out that what he thought was taco meat is actually toxic waste. After the line disconnects, a mysterious man calls with some information for the dean.

Leonard attacks an unsuspecting student and a full-fledged zombie attack ensues, terrifying the rest of the students. Dean Pelton leaves the library and locks all the doors in an attempt to quarantine the healthy ones, forgetting that the zombies are in there with them. He tells them that the Army is coming in to help in six hours. The healthy ones, meaning the study group, Chang, and Rich, barricade themselves in the group study room.

The group tries to keep the zombies away from the study room. Rich describes how the disease works. Annie suggests turning down the thermostat in order to break everyone's fevers. It is revealed that Rich is infected. Britta has also been infected. The others try to defend themselves from them, but Chang accidentally breaks the glass door with his ice skate and the zombie pour in. Jeff, Abed, and Troy escape to the basement in order to turn down the thermostat. Jeff is taken by the zombies and A... read more The group tries to keep the zombies away from the study room. Rich describes how the disease works. Annie suggests turning down the thermostat in order to break everyone's fevers. It is revealed that Rich is infected. Britta has also been infected. The others try to defend themselves from them, but Chang accidentally breaks the glass door with his ice skate and the zombie pour in. Jeff, Abed, and Troy escape to the basement in order to turn down the thermostat. Jeff is taken by the zombies and Abed sacrifices himself in order to let Troy get to safety. Meanwhile, Chang rescues Shirley and they hide in the bathroom, where they end up having sex. read less

Troy makes it outside and grabs the keys from Dean Pelton. He runs to the thermostat and even though he gets infected on the way, he bravely lowers the library's temperature. Everyone begins to come to, but the Army rushes in and drugs them all so that they don't remember anything about the night. Troy and Abed decide to watch Marmaduke together.

Troy hears a voicemail from Chang that was recorded just before the zombies took them. He tells him that he and Shirley had sex.