This post contains details from the Season 9 premiere ofThe Flashon The CW.
The Flashis nearly done fighting crime in Central City but not before one final villain comes to town.
But who could it be?

The FlashThe CW
I had a master plan for those two seasons.
The idea was bringing as many Arrowverse folks as we could.
So unfortunately, its not going to be soArrow-centric.

Although we do have a lot of guest stars, its gonna be veryFlash-centric.
Thats the important thing, to really honor Barry and Iris.
Now, thats become our series finale.
So, we are still getting to tell that very emotional, very special epic tale.
Its just a series finale.
DEADLINE: Im glad you mentioned the guest stars.
How did you develop the right stories for them to make one final appearance?
WALLACE:Everythings related to what would work for the story we wanted to tell in Season 9.
One is kind of a mentor figure and the other is a close friend to Barry.
Fortunately, it all worked out.
DEADLINE: In the premiere, we see Iris and Barry get stuck in this time loop.
WALLACE:It hits home.
Barry and Iris had the same fear, just opposite sides of the coin.
He is afraid of, how do I control my future?
Thats really the season theme that plays out over the rest of Season 9.
They dont survive by just wishing somethings going to happen in the future.
They dont survive or thrive certainly by dwelling only on events in the past.
You have to stick together and you have to do it in the moment.
You have to move forward moment by moment, second by second.
This episode is the introduction of their babymoon adventures.
Sometimes, well see it on camera, where they may go to an exotic locale.
They cant just be galavanting all over the planet all the time.
So all of that fits together to create what Im calling the season of romance.
Its the greatest romance the Arrowverse has seen.
That is the truth.
The question then becomes not only who is this person, but why are they here?
And what will they do as far as feeding intoThe Flash?
Folks arent going to have to wait long at all.
But her season long arc is a mystery about, Why is she here right now?
Ive talked to Danielle about this, and shes super excited.
But does she even know that?
Thats the journey shes on.
Its a journey of self discovery.
DEADLINE: So lets address the last scene.
Is Captain Boomerang working for Thawne?
WALLACE:Is that what we learned at the end of 901?
DEADLINE: I mean, thats what it seemed like to me, but thats why Im clarifying!
Now, youve hit upon something thats very critical.
Was that red lightning at the end?
But whos red lightning?
Well, the good news is for fans, youre gonna find out next week.
The thing about a short, accelerated season of 13 episodes is we dont have time to fool around.
We got to get to stuff pretty darn fast.
DEADLINE: What else can we expect from this final season?
WALLACE:I would say look for a lot more romance in Season 9.
So romance doesnt just apply to Barry and Iris.
It can apply to all of the characters.