Directed by: Mark Cendrowski
Story by : Chuck Lorre & Lee Aronsohn & Maria Ferrari
Teleplay by : Bill Prady & Steven Molaro & Steve Holland
Original air date: December 16, 2010
Penny gets back together with Zack. The guys insult Zack’s low intelligence which upsets him; however he reconciles with the four after Sheldon offers him Milk Duds and he accompanies them to the comic book store, where Stuart announces the New Year’s Eve costume party. The guys decide to come as the Justice League of America and also decide to include Penny as Wonder Woman (who initially refuses, but later agrees) and Zack as Superman (because according to Howard, “he is the only person we know with actual muscles”). Leonard dresses up as Green Lantern, Sheldon as The Flash, Howard as Batman and a reluctant Raj as Aquaman. Sheldon forces Penny to wear a black wig, as Wonder Woman has black hair, but Penny refuses to wear the wig and decides not to come to the costume party. Sheldon, Howard and even Zack are unable to convince Penny to change her mind. Later when Leonard talks to her in an attempt to convince her to come to the party, Penny reveals that she got back together with Zack only because she did not want to spend New Year’s Eve alone. Leonard questions why not with him, prompting Penny to suddenly remember the fun times she used to have with him, convincing her to change her mind and put on the wig. At the comic book store, the group win the award for the Best Group Costume, although it is hinted that they only won because they showed up with a girl. The episode concludes with the six witnessing an ongoing car theft and then scurrying off cowardly despite wearing Justice League costumes.