Barry accidentally arrives in Supergirl's reality after crossing a dimensional barrier while testing a tachyon accelerator with S.T.A.R. Labs, befriends Supergirl, and helps her battle against Livewire and the Silver Banshee, eventually returning to his world with Supergirl's help.
Barry accidentally arrives in Supergirl's reality after crossing a dimensional barrier while testing a tachyon accelerator with S.T.A.R. Labs, befriends Supergirl and informs her and her friends and allies the existences of the multiverse and metahumans. The Flash helps Supergirl battle against Livewire and the Silver Banshee, eventually returning to his world with Supergirl's help.