The “Supergirl” episode called “World’s Finest” brought The Flash (Grant Gustin) to Supergirl’s (Melissa Benoist) world in National City to help her restore her good side after she turned bad due to being influenced by a red kryptonite. The Hollywood Reporter notes that the events that transpired during Barry Allen’s stay in National City will be hinted at in “Flash Back,” an episode of CW’s “The Flash.” However, the two episodes of the shows will not appear chronologically because “Supergirl” airs on Mondays, while “The Flash” airs on Tuesdays.

That is the problem with the shows being in two different networks. “Supergirl” airs in CBS and “The Flash” in The CW. “The Flash” executive producer Greg Berlanti said that the audience has to “imagine they’re in parallel worlds, in different universes and the timeline is slightly different. One day ahead.”

According to the story of “World’s Finest,” Barry Allen runs so fast that he ends up on an alternate earth where Supergirl exists. Kara falls out of a skyscraper after Siobhan uses her Banshee cry and forces her out of the window. Flash does not know who she is yet and catches her. In superhero movies, people fall out of skyscrapers a lot, it seems. In the 1978 “Superman: The Movie,” Superman (the late Christopher Reeve) flies up to catch a falling Lois Lane (Margo Kidder). “Batman V Superman: Dawn of Justice” pays a great homage to that scene. However, Kara’s case is different.

Anyhow, Barry and Kara try to figure out how to get him back to his Earth and Barry decides to help Kara defeat the Silver Banshee and Livewire as they begin to wreak havoc on National City. The Flash and Supergirl fighting together are just any fanboy or fangirl’s dream come true.

Supergirl saves a helicopter from the electric bolts of Livewire but gets injured herself. It is here that we see our real-life heroes, the firefighters in action. They short circuit Livewire with their water cannons, who ends up incapacitating Silver Banshee instead. It’s rare in superhero movies to see humans being given much importance when superheroes are punching things around and cities turn into dust. “Supergirl” has done it wonderfully. One of the firefighters even tells Kara that it was their turn to save Supergirl.

There are a lot of light-hearted moments and some great humour in this episode. Barry brings ice creams for everyone in a split-second and everyone is super delighted, especially Kara, who exclaims “Yes!” Also, Kat Grant makes that meta comment of the “Supergirl” cast looking like “the attractive, yet non-threatening racially diverse cast of a CW show.”

There is also a twist. When Kara plucks up the courage to express her feelings for James, he gives no reaction to her kiss. It is revealed that the Myriad plan started by Astra (Laura Benanti) before her death is underway. Non (Chris Vance) has put all residents of National City under mind control.