The Flash is headed for Supergirl and the synopsis for the crossover is released by the network. The chapter will be titled, Worlds Finest, where Barry Allen from Central City will show up in Kara Danvers's National City.
Here is the synopsis released by CBS:
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.
Here are five things to expect in the mashup episode:
1. The crossover will happen in Supergirl season 1's episode 17, which will air on 28 March at 8pm EST on CBS.
2. The first promo art released pays homage to the cover for Superman #199 , which pitted the Man of Steel against The Flash in a race to determine who is the fastest. The picture released shows Flash and Supergirl racing, with a question, "Who is the fastest person alive?
3. There will indeed be a race between Kara and Barry in the episode as executive producer Andrew Kreisberg told Entertainment Weekly, "We do have a footrace, which is one of my favorite moments in this episode." The producer, however, did not say who will win, but instead teased fans by saying, "It's close."
4. Central City and National City will exist in an alternate universe, and Barry will be stranded in Supergirl's world following a time travel.
5. Kara and Barry will hit it off, as the Speedster will team up with the Kryptonian and help her defeat Live Wire and Silver Banshee. Also, Superman's cousin will help Barry get back home in the episode.