Supergirl: Behind-the-Scenes Featurette On The Flash Crossover (Mar 28)

supergirl,the flash
"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 at 8/7c." - CBS