Supergirl Season 1 Episode 18
Worlds Finest
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.
Guest Stars
Jenna Dewan
Lucy Lane
Chris Vance
Non
Brit Morgan
Leslie Willis / Livewire
Harriet Sansom Harris
Sinead
Grant Gustin
Barry Allen / The Flash