The guys get Zack and Penny to join their DC Comic Justice League of America costume group for a New Year's Eve bash at the comic book store to win the best group costume prize. Penny is going as Wonder Woman, while Zack dresses as Superman.
The guys discover that Penny and her ex-boyfriend, Zack, are back together and they take advantage of his lack of intelligence and make fun of him. After Zack finally realizes what's going on and storms out, the guys decide to apologize to him and give him some Milk Duds. Zack immediately forgives Leonard and his friends and goes with the guys to the comic book store, leaving a peeved Penny behind. At the store, the guys realize that Zack would be great as Superman for their Justice League group at Stuart's New Year's Eve costume party, who would replace the short Leonard as that role.
Leonard agrees as long as he goes as Green Lantern, leaving Raj to be Aquaman, much to his distress. They return home with the Justice League costumes, with Howard being Batman, Raj as Aquaman, Sheldon as The Flash, and Leonard as Green Lantern. They even purchase a Wonder Woman costume for Penny. However, Penny doesn't want to go and suggests that they ask Bernadette or Amy, but Howard says Bernadette is under quarantine and Sheldon says Amy doesn't believe in wearing costumes, leaving no choice, but for Penny to go.
On the night of the party, the guys arrive at the apartment in their costumes. Sheldon as the Flash is pacing back and forth though Leonard says that it looks like he's jogging. Sheldon replied by saying, "This is how The Flash paces". Howard enters proclaiming "I'm Batman". Raj thinks that Aquaman stills sucks. Zack leaps into the apartment as Superman, but can't remember, "It's a bird. It's a plane. It's Superman." Penny enters in her sexy Wonder Woman costume and refuses to wear the black wig. Howard that no one will be looking at her hair (glancing at her cleavage while he says it) and gets punched by Wonder Woman. Finally she refuses to even go to the New Year's Eve costume party at the comic book store after Zack embarrasses her. None of the guys, not even Zack, can convince Penny to go. Since Zack would not go without Penny and the Justice League wouldn't be complete without Superman and Wonder Woman, Sheldon says that they'll have to go in their Muppet baby costumes, but then they make Leonard talk to Penny.
Penny reveals that she is only with Zack because she doesn't want to be alone for New Year's Eve. It is hinted that she still hasn't fully gotten over Leonard. Penny relents, puts the wig on to avoid the "Leonard" question, and the group later wins the costume contest. Sheldon demands that he make his victory speech, however, Stuart interrupts him and lead the countdown to midnight.When midnight strikes and it becomes the New Year, 2011, Zack is kissing Penny, she looks guiltily over at Leonard for the duration of the entire kiss, while Leonard gazes back at her. The episode concludes with the group witnessing an ongoing car theft on the way back home and despite wearing Justice League costumes, they comically scurry off. None of them, not even Zack, are brave enough to stop the car theft.
That New Year's Day evening, Leonard warns Sheldon that he wants to change the thermostat temperature. Sheldon then imagines himself as The Flash, speeding to the Grand Canyon to scream in frustration, to the tune of "Flight of the Bumblebee". Once he is "back," Sheldon tells Leonard, "Fine."
- Guest starring:
- Teleplay: Bill Prady, Steven Molaro & Steve Holland
- Story: Chuck Lorre, Lee Aronsohn & Maria Ferrari
- The TV Critic: "This failed on pretty much every level which was a shame. In theory I applaud the idea of focusing on Penny and Leonard's relationship, but there is no authenticity to it anymore. The writers have made less and less effort to demonstrate any actual bond between them. Leonard still treats her like she is too good for him and her feelings for him have returned out of nowhere. The result is that her emotions seem fabricated and the story falls flat...What often saves The Big Bang Theory from being a lame duck is the sharpness of its writing. In this case the writing was lazy and the result was a lousy episode which felt as phoned in as Penny's feelings for Leonard." 
- The A.V. Club gave this episode an A-.
- IMDb user reviews
- Title Reference: The title refers to Sheldon, Leonard, Howard and Raj inviting Penny and Zack to be Wonder Woman and Superman, respectively, in their Justice League team and Zack replacing Leonard for Penny.
- Chuck Lorre's vanity card.
- This episode was watched by 13.24 million people with a rating of 4.0 (adults 18-49).
- This episode aired in Canada on December 16, 2010 with 3.021 million viewers and a weekly ranking of #1.
- In the United Kingdom, this episode aired on January 13, 2011 with 1/038 million total viewers and a weekly ranking of #19.
- Episode transcript 
- Bernadette and Amy are mentioned by name, but are both not seen with any appearances in this episode because Melissa Rauch and Mayim Bialik both don't get credited to appear as main cast members in the apartment scenes and the Comic Store New Year's Eve Party scene this episode. They are both absent in the next episode (S4E12).
- As of this episode Bernadette and Amy are the only ones in the gang that don't dress up as comic superheroes because these were not required for the storylines in this episode.
- Bernadette did not appear as Blonde Phantom in the apartment scenes and the Comic Store New Year's Eve Party scene in this episode because it was not written and included in the storylines of this episode.
- Amy did not appear as Catwoman in the apartment scenes and the Comic Store New Year's Eve Party scene in this episode because it was not written and included in the storylines of this episode.
- The Justice League consists of
- Sheldon asks in what universe is Wonder Woman blonde, in fact Cathy Lee Crosby starred as a blonde Wonder Woman in the 1974 TV movie "Wonder Woman" Also in a Teen Titans storyline "Titans Tomorrow" Cassandra Sandsmark aka Wonder Girl, who was a blonde, was shown as Wonder Woman's successor.
- Raj once went to a cricket (game) camp, and had a penis drawn on his face by bullies there. Refer to "The Speckerman Recurrence" for more on bullies.
- Stuart reveals that he earns around $1.65 an hour, $6.35 below the minimum wage in Pasadena, California. This is likely not a legal breach, as Stuart owns his own business and therefore is not entitled to a minimum wage. Nonetheless, this suggests he has low profits, and would probably be significantly better off working for pay even in a menial job.
- Raj hates Aquaman in this episode. In "The Spaghetti Catalyst" (S3E20), Raj stated, "Oh, please, we all know I’m the friend you call when you have no other options. If we were the Justice League, I’d be Aquaman." He also mentioned Aquaman in "The Precious Fragmentation" (S3E17) and "The Robotic Manipulation" (S4E1).
- Some species of sea star have the ability to regenerate lost arms and can regrow an entire new arm in time. Sea stars can grow an entire sea star from a single ray.
- Coaches use the expression, "There's no "I" in team", which is probably where Zack got his response to Penny from. "There's no "I" in Justice League."
- Bernadette is under quarantine for this episode, as at her lab Christmas party she took Jell-O shots from a petri dish that used to contain Yellow Fever. This fact was revealed by Howard when the guys asked why she couldn't be Wonder Woman. That is why Bernadette is not featured in this episode
- Sheldon says that Amy does not wear costumes, but she did in later episodes though she has been more willing to change than Sheldon. That is why Amy is not featured in this episode.
- When Penny is talking to Leonard in her apartment, this time is the closest that she ever comes yet to telling Leonard how much she feels for him. Penny refers to "The Middle-Earth Paradigm" (S1E7) when she states to Leonard, "Look, if Zack and I had just gone to a regular club or a party, it would have been fine, but this, with the costumes, and you."
- Penny's dislike for costume parties at the comic book store is brought up again in "The Holographic Excitation" (S6E5).
- The costumes the cast choose reflect their character:
- Howard as Batman - Howard is an engineer and has built a lot of high-tech gadgets, such as an engineer might make.
- Raj as Aquaman - In comic books Aquaman is the King Of Atlantis and spends a lot of time being classified as an outsider. Raj as a foreigner sometimes doesn't understand American culture and is an outsider in other ways.
- Penny as Wonder Woman - Fairly self-explanatory. She is Leonard's Wonder Woman.
- Leonard as Green Lantern - Green Lantern is a character who uses a ring to create constructs using their will. Green Lantern users therefore must have a lot of will to be successful. Obviously Leonard has the will to work hard in his studies to become a Doctor. What is relevant though is that Leonard must have great will to put up with Sheldon.
- Zack as Superman - He is the only one out of the group to have actual muscles.
- Stuart's costume is that of the Fourth Doctor (originally played by Tom Baker) from British cult sci-fi TV series Doctor Who. Stuart's DJ's costume is "Master Chief Petty Officer John-117", a "SPARTAN Programme supersoldier" and the main protagonist of the Halo video game franchise.
- Other costumes at the party (not counting duplicate Justice Leagues) include a woman dressed as a Hogwarts student (likely Hermione) from the Harry Potter book/movie franchise, an Imperial Stormtrooper and a Jedi (possibly Ben Kenobi as he appears in A New Hope) from the Star Wars franchise, a Joker from the Batman franchise, a woman dressed as a sciences crewman (or possibly a nurse) from Star Trek the original series, and what appears to possibly be Hagrid the groundskeeper, again from Harry Potter.
- The distance from Pasadena to the Grand Canyon is approximately 500 miles by road, some 375 miles straight-line.
- When Leonard knocks on Penny's door to talk to her, Penny does not recognize that it's not Sheldon's Knock being knocked on her door and she responds "Go away, Sheldon." until Leonard says it's actually him.
- Penny: No. I'm not wearing it. It looks stupid.
- Penny: Forget it. I'm not wearing the wig
- Zack: Oh, no, you’re thinking old-school Archie. It’s much more sophisticated now. Like, there’s two universes, and Archie’s married to Betty in one and Veronica in the other. Midge is even breaking up with Moose.
- Leonard: Look, I know our winter thermostat setting is 72 degrees, but I'm a little warmer, so I'm going to turn it down.
- Sheldon: (as The Flash, runs to the Grand Canyon) Good lord, how you frustrate me, Leonard Hofstadter! (runs back) Fine.
- Zack: Look up in the sky. It’s a bird. It’s a plane. I forget the rest.
- Penny: All right. Let’s get this thing over with.
- Sheldon: I’m sorry. But in what universe is Wonder Woman blonde?
- Howard: Relax. No one’s going to be looking at her hair. Ow! I mean, "OW!"
- Sheldon: (knocking door loads of times) Penny, Penny, Penny, Penny, Penny, Penny, Penny, Penny, Penny, Penny, Penny, Penny, Penny, Penny, Penny, Penny, Penny, Penny, Penny.
- Penny: (opens door) What the hell is wrong with you?
- Sheldon: I'm the Flash. I just knocked 30,000 times.
- Penny: Are you high?
- Raj: What the hell did I do?
- Penny: You laughed.
- Zack: Milk dud?
[Penny’s apartment. Knocking.]
- Penny: Go away, Sheldon.
- Leonard: It’s Leonard.
- Penny: Oh. Go away, Leonard.
- Leonard: Come on, let me just talk to you
- Penny: It’s open.
- Leonard: Hey.
- Penny: I’m not going to that party, Leonard
- Leonard: Okay, listen. You don’t have to wear the wig. At this party, we’re gonna win first prize just by showing up with a girl.
- Penny: It’s not the wig.
- Leonard: Did I do something? I mean, I tried to be friends with Zack, like you said, which believe me, was difficult, given how you and me used to be, you know, you and me, and now you and him are you and him.
- Penny: Okay, look. We’re not really me and him.
- Leonard: Then what are you?
- Penny: I don’t know. I only started seeing Zack again so I wouldn’t be alone on New Year’s Eve. How pathetic is that
- Leonard: Not as pathetic as dressing up like this and going to a comic book store on New Year’s Eve
- Penny: You make a cute Green Arrow.
- Leonard: Green Lantern.
- Penny: Like there’s a difference.
- Leonard: There’s a big difference. Arrow. Lantern.
- Penny: Whatever. Look, if Zack and I had just gone to a regular club or a party, it would have been fine, but this, with the costumes, and you.
- Leonard: What about me?
- Penny: Nothing. Let’s go to the party. (Puts on wig) How do I look?
- Leonard: Um, I guarantee you’ll be the prettiest girl there.
[outside the door]
- Howard: Okay, the good news is, we have a Wonder Woman.
- Sheldon: Oh.
- Zack: Yes.
- Sheldon: What’s the bad news?
- Howard: Superman probably isn’t getting laid tonight.
- Zack: Aw, damn.
- ↑ The Big Bang Theory - The Justice League Recombination (TV Episode 2010) - IMDb
- ↑ The TV Critic's Review
- ↑ The Big Bang Theory: "The Justice League Recombination" - TV Club - The A.V. Club
- ↑ Thursday Final Ratings: Big Bang Theory, $#*! My Dad Says Adjusted Down - Zap2it
- ↑ Top Programs – Total Canada (English) December 13 – December 19, 2010 - BBM Canada
- ↑ BARB via Wikipedia