Kara tells the Super Hero Girls and three of the Invinci-Bros, Hal, Barry and Garth, at the secret base about the band League of Shadows performing at the Lazarus Pit club. Karen also tells them about the band Up Past 8 and says she has tickets to their concert. When nobody wants to go to either of their concerts, Kara decides to take Karen to the League of Shadows live show, and gives her a punk-rock makeover, much to Karen's distaste. At the show, Karen continues to feel uncomfortable about the atmosphere, and Kara is invited backstage where she meets Ra's Al Ghul and the other band members of League of Shadows. Ra's gives Kara the "Demon's Fang", a red, glowing guitar pick. Later, on stage, Ra's sings Kara a song, and the lyrics allow the Fang to possess Kara's soul and make her an evil servant for Ra's.
Karen returns to the secret base and throws away her makeover clothes, returning to her old self. Kara arrives shortly after with red irises and wearing the Demon's Fang on a choker. She disrupts all the other girls' and boys' activities, acting incredibly rude and then flies away. Karen notices her tickets for the Up Past 8 concert are missing and suspects Kara took them. She follows Kara and sees her using the tickets to get into the Up Past 8 concert. Karen transforms into Bumblebee, and goes miniature to sneak into the concert. She spots Ra's with the rest of the LOS and hears him telling his acolytes that he controls his new weapon with "a stone from outer space", and plans to control Kara to destroy several atrocities, the first being bad pop music. Bumblebee uses her wrist computer to analyze the Demon's Fang, revealing that it is of Kryptonian origin, and that red kryptonite causes, among other things, "susceptibility to mind control" in Kryptonians. Bumblebee decides that in order to stop Ra's and his plans, she must call for help. Later, the concert is about to begin, and as the lights turn on with the silhouettes of what appears to be the members of Up Past 8 appearing, Ra's forces Kara to transform into an evil version of Supergirl through their pieces of red kryptonite to destroy the band. However, it turns out that the boys on stage are Hal, Barry and Garth dressed in the white Up Past 8 clothes, while Bumblebee ties up the three actual band members backstage in their undergarments. The boys sing Let Me Save You With My Love while Kara attempts to attack them repeatedly as the rest of the Super Hero Girls try to stop her. Eventually, Bumblebee discovers that Supergirl's got Ra's' mind-control song stuck in her head and "the only way to get it out is to hit her right in the heart", and informs this to Hal. Hal, Barry and Garth sing the bridge of the song, which is coincidentally ties into snapping Supergirl out of the trance, while the other Super Hero Girls hug Supergirl tightly. Garth's high-pitched note causes the Demon Fang to break, forcing Ra's to retreat, and Supergirl lands on stage and starts dancing to the rest of the song alongside the other Super Hero Girls, Hal, Barry and Garth.
Although this special consists of the forty-third and forty-fourth episodes, they are the thirty-fifth and thirty-sixth in production order.
Aside from gasping and laughing, Barbara does not any spoken dialogue in both episodes.
Kite-Man appears briefly in the cameras that Babs uses to spy on while he is negotiating with a gangster, whose appearance seems to allude to the Joker.
This could be reinforced to his outfit, which resembles Jack Napier's, the name used for Jack Nicholson's Joker from the 1989 Batman movie.
Due to a disagreement on airing this episode in Canada between STACKTV and Corus Entertainment, this episode did not air in Canada until February 7, 2021.
During the beginning of the episode, when Barry Allen was eating popcorn, his movements are similar to how he ate popcorn in Teen Titans Go! To the Movies.
The plot of this episode somewhat resembles that of My Little Pony Equestria Girls: Rainbow Rocks, which is based on My Little Pony: Friendship is Magic, a franchise in which Lauren Faust was involved.
A building named "Metropolis Gardens" at the ending of Part 2 is a reference to Madison Square Garden, an arena located in New York City in the United States.
Since the episode "Breaking News," Zatanna is seen shooting magic using her fingers, like a gun.