[Barry Allen is explaining to the others about the multiverse and how he arrived.]
BABarry Allen
[drawing circles on a whiteboard] All right. So imagine there are multiple versions of Earth. One where, uh... the Nazis won World War II , one where Kennedy was never assassinated...
[raising a hand like he's in a classroom] Okay, one where all of us are evil.
Barry
Been there. It sucks. So all of these Earths occupy the same place in space, but they vibrate at a different frequency, so they can't see one another.
Yeah, yeah, but it's like, if you can go fast enough, then it's possible to open, like, a breach and then travel between worlds.
Barry
Yeah.
But how could you travel that fast?
Barry
[amused] Uh, well, um...
[Barry races out of the room at super-speed, then returns seconds later, giving each of them an ice cream cone.]
Barry
Yeah. So, um... I was struck by lightning the same night a particle accelerator exploded, and I became a... superhero.
[Kara giggles, impressed and a little smitten.]
So, so, so... y-you're a superhero, too.
Barry
Mmm-hmm.
[subdued] Tha-that's cool, I guess.
When I was helping people as Supergirl, I was... I was so happy. And now that the people don't want me to help them, I feel lost. And I'm in such a hurry to prove myself again, I'm making stupid mistakes, like today.
Barry
This is going to sound ironic coming from me, but you need to slow down. Just keep doing your good work. Don't worry about the rest. The public will forgive you, I promise.
Barry
'Cause the same thing happened to me.
Barry
Mm-hmm.
So what finally fixed things?
Barry
Time.
[Barry and Cisco appear through a dimensional breach in Kara's apartment.]
CRCisco Ramon
This better be the right place. 'Cause if this isn't the right place, someone's about to be real confused.
[Kara comes in the front door.]
Barry
Hey.
I knew it. I knew that was you. I knew that it was you and that weird space portal thing! [hugs Barry] Hi.
Barry
Yeah. I'm sorry. It took a couple tries to get here. This is my friend Cisco.
CCisco
Well, "friend" is a loose term. We work together. Hi. I have to say it, this is a nice universe you got here.
Barry
Okay, do you remember last year, when I helped you out and you promised to do the same for me?
Story continues in Invasion! (Arrowverse).