During the party, a few of the partygoers become sick from eating a hazardous substance that the dean mistook for taco meat bought at an army surplus store.
As the study group try to escape, the dean (under orders from U.S. Army Special Operations) locks the doors, trapping them inside with the infected.
The pair walk inside, where all the songs being played are by the 1970's pop group ABBA and Pelton's voice notes to himself, as they are using his iPod for the music.
When Pierce asks Dean Pelton (Jim Rash), dressed as Lady Gaga, where he got the food, Jeff reveals it is old military rations bought at a surplus store.
Annie (Alison Brie) finds Rich (Greg Cromer), the doctor from the beginner pottery class,[a] and they discover that Pierce is running a temperature of 102°F.
While Troy (Donald Glover) and Abed (Danny Pudi) attempt to court women with their Aliens-inspired costumes, other partygoers begin contracting the mysterious sickness.
Troy, who has by this time changed out of his science-fiction style costume and opted to dress as a “sexy Dracula,” calls Abed a nerd, hurting his feelings.
At the party, Leonard (Richard Erdman) savagely bites a woman, and Troy and Abed realize that they are in the midst of a zombie attack.
When they begin exhibiting symptoms, Chang (Ken Jeong) throws an ice skate at them to knock them out but ends up breaking a window, allowing the zombies to surge in and grab Annie.
The following songs by the Swedish pop music group ABBA are featured throughout the episode: "Waterloo", "SOS", "Dancing Queen", "Gimme!
[1] Series creator Dan Harmon later stated on his Twitter account that he paid for the changed opening credits himself, as it wasn't in the network's budget.