[MILD SPOILERS for The Flash/Supergirl crossover episode ahead.]
CBS' Supergirl TV show has already seen Kara Zor-El/Danvers (played by Melissa Benoist) join forces with another DC Comics superhero (and no, not her famous cousin): J'onn J'onzz a.k.a. Martian Manhunter, who passes himself off as being Hank Henshaw (David Harewood), the human head of the Department of Extranormal Operations (or DEO) organization that Kara and her adopted sister, Alex (Chyler Leigh) work for. However, Kara will soon be fighting super-villains alongside another DC stalwart altogether, as Gran Gustin's Barry Allen from The CW's The Flash will soon be making a trip to National City - which, it turns out, exists as part of the larger Multi-verse that has served as the crux of the narrative for The Flash season 2.
The Supergirl/Flash crossover episode is titled 'Worlds Finest' and was co-written by Supergirl series writer/producer Michael Grassi, along with Greg Berlanti and Andrew Kreisberg - the latter duo, of course, also being the co-creators of both DC TV shows and the head executive producers on the series too (alongside such folk as Supergirl co-creator Ali Adler). So far, it appears that 'Worlds Finest' will be structured as a one-shot adventure for Barry and Kara, though the episode's newly-released official synopsis confirms certain story details - namely, those which had previously only been made available thanks to leaked set photos from the episode's shoot.
EW has the exclusive on the 'Worlds Finest' synopsis, which reads as follows:
Kara gains a new ally when the lightning-fast superhero The Flash suddenly appears from an alternate universe and helps Kara battle Siobhan, aka Silver Banshee, and Livewire in exchange for her help in finding a way to return him home.
In addition, EW has premiered an official poster for the Supergirl/Flash crossover, which you can check out below. The 'Worlds Finest' artwork here is an homage to the cover for Superman #199 - which, by comparison, pitted the Man of Steel against The Flash in a race to determine who is fastest - similar to how the poster released for The Flash season 2 (featuring Barry Allen and Jay Garrick) was a shout-out to the famous comic book cover for The Flash #123. There will indeed be a race between Kara and Barry in 'Worlds Finest' and Kreisberg told EW that it's "one of my favorite moments in the episode." Kreisberg, naturally, remained mum on who wins the race though, simply saying "It's close."
Supergirl explores the responsibilities that Kara must deal with as not only a superhero who is trying to prove her worth in a world that already has Superman, but as a female superhero (and the pressures that come with the job), at that. However, both The Flash and Supergirl have similarly upbeat, optimistic and overall more playful tones that allow them to explore meaningful subject matter and/or familial drama, while at the same time incorporating such outlandish DC Comics supervillains as King Shark and Silver Banshee (Italia Ricci), among others, into the mix without their presence feeling out of place. For that reason, a crossover between the two shows not only feels appropriate, it has the potential to make for an especially fun Supergirl episode too - regardless of whether or not it paves the way for future crossover adventures featuring Kara and characters from other CW/DC TV shows (see Arrow and Legends of Tomorrow).
Who knows - if there's a next time, maybe we'll even get that Flash/Supergirl musical crossover episode we wanted after all?
Supergirl season 1 continues with ‘Falling’ on March 14th on CBS. The Flash season 2 continues with ‘Trajectory’ on March 22nd on The CW. The Flash/Supergirl crossover episode 'Worlds Finest' will air on March 28th on CBS.