Conversation so far:
when does the flash show up in supergirl
Worlds Finest, the eighteenth episode in the first season of the CBS television series Supergirl, features an appearance by The Flash
when does the flash reveal his identity in the eighteenth episode of supergirl
The speedster introduces himself as Barry Allen, a.k.a. the Flash, after Kara reveals herself as Supergirl in the 18th episode of season 1 of Supergirl
did cat know the flash's identity in the 18th episode of supergirl
In the 18th episode of Supergirl, Cat reveals to Kara that she knew Barry Allen was the Flash all along.
who plays barry allen in supergirl
It was announced that Grant Gustin, who appears as Barry Allen on The Flash, would appear in the eighteenth episode of the first season of Supergirl.

Question: how does barry go back home
Self-contained rewrite: how does barry allen go back home in supergirl season 1, episode 18