Getting tired of how James has always put their relationship second to his job and crime fighting, Lucy has broken up with him before leaving the city. Alex is trying to get Kara to admit her feelings to him now she has a chance, and Senator Crane has returned to get them more funding for the DEO to keep them working.

And some sorta strange interaction between Crane and Hank makes it seem as if she might like Hank.

They stop talking when they get told theirs a fire and a fireman trapped. Peter and Kara race to help them and as they get there, Kara takes care of the fire and Peter lifts up the rubble to get the fireman free.

The two take care of business and get cheered on by the firemen and citizens. But as soon as they start leaving, Peter's senses warn him of something and his head starts going fuzzy.

He then sees Kara take off and decides to scan the area of anything and finds something underneath the rubble and it looks almost like a different type of kryptonite. And this one feels like it's actually doing something to him, unlike green Kryptonite.

"I better bring this back to the DEO." Peter states and takes off for the said DEO.

On Kara's side, the Red kryptonite has unintentionally affected Kara and she doesn't even know it as her attitude is changing slowly. Not knowing she was affected by the Red kryptonite.

-

"Two armored vehicles have been attacked in the last six hours. Both carrying hundreds of thousands worth in gold." Hank is telling everyone as Peter is holding onto the substance until he's done, wanting to hear this. "Now, these two have goons managed to take out a number of highly trained and heavily armed security personnel."

"Alien weapons?" Alex asks.

"Almost. An alien is their weapon." Hank says and pulls up the photo of someone that looks like an older man with a robot eye. "A K'hund. Stronger than your average Fort Rozz prisoner. We've obtained intel on their next heist, but we have to move fast. Lucky for us, we have two of our own." He says looking to Peter and Kara who's sorta slacking on the table.

"You doing okay, Skirt?" Peter asks, never seeing her act like this before.

"Am I boring you, Supergirl?" Hank also asks her.

"Only boring people get bored." Kara tells him. "I'm sorry, thought you were talking about some other alien in the DEO." She says before spinning in the chair.

"I'm gonna go drop something off with Gwen, I'll be right with you, Hank." Peter promises before going into Gwen's lab and dropping off the Red substance.

"What's this?" Gwen asks while looking over the substance.

"It was something I found on the roof. My senses seemed to think it was dangerous, and it looked a lot like our stash of kryptonite we have." Peter explains. "I was hoping that you could tell me if it could have any different affects to kryptonians than regular kryptonite."

"I'm your girl." Gwen says and walks off to run some tests. "Let's see what makes you glow. Literally." She tells the substance while walking away.

"She's talking to rocks now. God, I love her." Peter mumbles chuckling before walking out to find Hank to stop these thieves and the K'hund.

-

That night, another heist was going on and the K'hund was there when the DEO intervened. He leaps away and the two heroes go flying to stop him from getting away.

"Your parents..." the K'hund was saying but Kara interrupts him.

"Scentenced you to Fort Rozz, blah, blah, ruined your life, heard the story." Kara tells him. "You wanna fight about it?" She asks as he comes up to attack them but Peter blasts him back with his repulsers and Kara slams him against the wall.

"I have defeated White Martians, Coluans and kryptionians. You're not even worth looking at." Kara states to him, getting seriously cocky before Peter pushed her off of his throat and slapped the power handcuffs on him.

"Me and you need to have a talk when we get to the DEO." Peter tells Kara, trying to figure out what's going on with her.

"Oh, that sounds like fun." Kara says, each word dripping with sarcasm as the DEO agents, lead by Alex, make it to their location and arrest the K'hund.

-

They return to the DEO and as they're walking the K'hund to his cell, Peter drags Kara somewhere more secure to talk alone.

"I know you're going through a tough time with your aunt and everything, but our job is to stop Alien criminals, not crush their necks." Peter informs her.

"How about you get off my back for once, Peter?" Kara asks her.

"I thought you were getting over what happened to your aunt after everything with Indigo." Peter replies.

"We're in a good place, when I do what you tell me to do. When I don't, you act as if it's the end of the world. You might've started this before me, but I'm three times stronger than you!" Kara informs him.

"Five times, actually." Peter corrects her, keeping calm.

"Well, I've gotta get going. I've got another job that under appreciates me." Kara states while leaving.

On her way out, her face started glowing red and she slams her fist into the wall, breaking it.

For Peter, he starts feeling dizzy and it's as if something is waving through him.

He then makes it to Gwen's lab and prays she found out what that substance is doing to him.

"Did you find anything about the substance?" He begs of her.

"Well, it is definitely not from the periodic table, meaning it's alien. But parts of it us actually human, manmade." Gwen tells him as she's running more tests and Hank enters the labs to figure out what happened with Kara. "It doesn't damage kryptonians on a cellular level. It seems to be doing something different, I just don't know what." She explains.

"Who would make kryptonite?" Hank asks when Maxwell Lord is being escorted by guards to their lab.

"That's my bad." Lord tells them.

And that was all they needed to hear, this time they're locking him back up this time for good.

"Come on, I came here to help. I didn't even know kryptonite was a thing." Lord admits.

"Until we showed you." Alex corrects him while closing the cell.

"When we tried to take down Bizarro with said kryptonite." Hank finishes.

"I went through all that trouble to create her, when all this time, right in front of me, was a substance whose sole molecular purpose was to kill Kryptonians. Sort of ironic." Lord tells them.

"Do you have any idea what it even does?" Peter asks him.

"You've been affected by the synthetic K as well, haven't you?" Lord asks Spider-Man.

"Not in the same way as Skirt." Peter states. "What will it do to Kryptonians?"

"I was tracking the two of you to see what the Red kryptonite would do to either of you. It seems to just make you confused, a bit disoriented. While on Supergirl's end, she recently threw Cat Grant off her building." Lord tells them.

"She's dead?" Winn asks, as Hank called him in with James.

"No, Cat has nine lives. She's fine. I'm here to make things right. I created Red kryptonite, maybe there's a way to make an antidote." Lord says and they look to Gwen.

"You having any hope with doing that?" Peter asks Gwen.

"If he knows how to make red kryptonite and way it does, it'll save some time." Gwen says and Hank lets him out of the cell.

"You turned Supergirl into the monster you feared she'd become. So if you can't fix her, I'll become the monster you feared." Peter warns him.

"What do we do if she starts attacking people?" Alex asks and Peter looks to Gwen.

"It's time to get out the Kryptonian-Slayer." Peter tells her.

"What's the Kryptonian-Slayer?" Alex asks, not understanding.

"It's what I created for when this day were to come." Hank tells them, happy to see if Gwen's creation is getting put to use.

Cat Grant gives a warning to the city of how Supergirl has changed to the dark side and the city seems to have changed against her.

Alex goes to check on Kara to find she's even changed her outfit to a completely dark suit and she tries to talk to sister down but all she gets is angry replies about how powerful she is compared to Alex.

Kara then plans to get out there and make the city kneel below her.

"You need to use everything the DEO has and protect this city from Supergirl." Crane tells them at the DEO and they slightly agree.

Peter then comes out wearing a completely different suit than his Iron-Spider suit. This one is completely silver with his familiar design on it and most of the rest that isn't armored is filled with black cloth.

"That's why I invented this." Peter tells them. "It's made out of promethium, which is the strongest thing it could've been created from. It's also embedded with kryptonite, not enough to kill her, but weaken her enough to level the playing field." He explains.

"This should help you." Lord says and he brings out a syringe with the serum to bring Kara back to normal.

"If you are wrong, and I have to do something worse to Supergirl, I'll be coming for you." Peter warns Lord again before leaving.

-

Kara is heading though a report of Cat Grant on the screens of the streets and smashes into it and the police start shooting and she just laughs.

As they're fighting, they all look to see Spider-Man coming in swinging (Gwen never had the chance to attach the repulsers to this suit) and he lands down the street from Kara.

"Everyone, stand down, now!" Peter tells the officers and they all start standing down. "Skirt, you listen to me. You've been exposed to a dangerous substance. It's making your mind go whacko. You have to stop this."

"Nothing can stop me." Kara says before speeding off and slamming into Peter and dragging him through the Catco building. Kara sends a powerful punch and slams Peter through the office.

"Why am I getting a sudden case of déjà vú?" Peter suddenly asks himself while he has a second.

I mean, this feels all too familiar to him for some bizarre reason. He's fighting someone who's more powerful than him, who's lost control of themselves because of mind control. Where has he seen this before?

Before he could put more thought into it, Kara grabs Peter again and slams him against the wall.

"You are...weak! I am more powerful than you could ever become." Kara informs Peter.

"Yeah, well, we never talked about one power I have. Surprise." Peter states before he takes out the syringe and injects it onto Kara and she looses control of herself and falls.

Peter then flies after her and catches her. But that was a mistake as it seems she broke something of his and he starts swinging back to the DEO with a broken arm.

-

Kara later wakes up in the DEO and looks around. "Did I kill anyone?" Kara asks Alex.

"No, nobody was hurt." Alex informs her sister. "Peter's arm is a bit broken but he'll live." She promises and Kara breaks down after everything comes back to what she said and starts apologizing to Alex about what she said.

"There's truth behind what you said." Alex states and knows they need to work on what that is.

-

"Well, we now know that the Kryptonian-Slayer needs some work." Gwen says as Peter has his hand in a cast.

"Yeah, that armor was strong enough to stop Skirt." Says Peter agreeing with her.

"Its a good thing you were able to get through to her when you did." Gwen says and kisses him, happy he was able to at least survive.

Kara now knows that she needs to work the city's trust back, and that could be really hard, considering what she did. But she knows it'll be better when she's able to get the city's trust back.

And during her time on the dark side, Kara was able to get the new assistant Leslie fired, that's how Winn learned that she apparently has a screaming ability.

But what both of the heroes don't know, is that there's a man in red coming to prove their not alone in the multiverse.