In this promo for next week's episode of "Supergirl," titled "World's Finest," Barry Allen finds his way to National City. While "The Flash"/"Supergirl" crossover was announced recently, this is the first promo to show these two heroes working side by side.
“Worlds Finest” – Kara gains a new ally when the lightning-fast superhero The Flash (Grant Gustin) 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, on SUPERGIRL, Monday, March 28 (8:00-9:00 PM) on the CBS Television Network. Grant Gustin crosses over as The Flash.
"Supergirl" airs Mondays on CBS at 8 p.m.