CBS has revealed the first poster for the upcoming crossover between “Supergirl” and The CW’s “The Flash,” as well as the plot details for the episode, airing March 28.

Titled “Worlds Finest,” the hour sees titular heroine Kara (Melissa Benoist) gain a new ally when the lightning-fast superhero The Flash, aka Barry Allen (Grant Gustin) suddenly appears from an alternate universe. Barry helps Kara battle Silver Banshee, aka Siobhan Smythe (Italia Ricci), and Livewire (Brit Morgan) in exchange for her help in finding a way to return him home.

The Scarlet Speedster already has some experience with alternate universes, having paid a visit to Earth-2 — another version of our world, albeit with some striking differences — in Season 2 of the CW series. During that trip, “The Flash” teed up the impending crossover by including a shot of Benoist’s Supergirl while Barry traveled through the breach between worlds, hinting at a larger DC Comics multiverse that offered endless possibilities on infinite Earths.

While Supergirl and Superman don’t exist on Barry’s Earth-1 — which is set in a continuity known as the “Arrowverse,” since it encompasses all of the superhero shows spawned by The CW’s “Arrow,” including “The Flash,” “DC’s Legends of Tomorrow” and animated series “Vixen” — Barry’s ability to travel through time and space means that he’s capable of paying a visit to other DC Comics-based shows (even on other networks) without disrupting anyone’s reality.

Check out CBS’ newly-released poster for the crossover episode below, which is an homage to DC’s “Superman” issue 199, which saw a race between The Flash and Kara’s cousin, the Man of Steel.

And take a look back at the first time Gustin and Benoist united — to help celebrate executive producer Greg Berlanti for Variety‘s cover story.

“Supergirl” also stars Calista Flockhart, Chyler Leigh, Mehcad Brooks, David Harewood and Jeremy Jordan. The story for the episode hails from Berlanti, with the teleplay penned by executive producer Andrew Kreisberg and Michael Grassi. “Worlds Finest” was directed by Nick Gomez.

“Supergirl” airs Mondays at 8 p.m. on CBS; “The Flash” airs Tuesdays at 8 p.m. on The CW.