They were just testing Mon-El's powers, while he explains to them that he was supposed to get the prince of Daxam off the planet before it exploded, but the prince made Mon-El leave so he could share the fate of his people.

After assessing his powers, Kara had offered to help him be more human as the team at the DEO get him everything he's going to need and got him a place at Catco.

Peter was swinging through the city when Gwen warns him that there's a robbery taking place and Kara is already at the scene.

Once he gets there, Kara has already changed and he sees these guys have guns and bigger weapons.

"You do know those bullets aren't going to work on me, right?" Kara reminds them.

"I'm glad I didn't bring any bullets." One of them says and raise their weapon that shoots blasts of electricity sending her flying.

James, who was with Kara when it happened, tries to help but is beaten when Peter comes flying in and blasts his repulser at one of the to get stopped by the weapon.

Peter tries it with both of his hands and it does nothing as another goon shoots him in the back, sending him flying.

"Okay...that hurts." Peter says as he tries getting up after that blast he felt even through the nanotechnology.

-

At the DEO, Gwen identifies the weapon as an Anndrannian Photon Cannon.

"How'd these guys get their hands on alien technology?" J'onn wants to know.

"Are you sure they weren't Anndrannian? Alex asks them.

"Well, they weren't purple with fins, so I'm sure." Kara informs her.

"Well, you're lucky you were hit before it was fully charged." Gwen tells her. "This thing has the ability to erupt planets to their core. No telling what it could do to Kryptonians."

"Well, whatever they are, we gotta find a way to stop them and the weapons." Peter interjects.

"So it emits phased muon particles. I could come up with a way to detect it." Winn offers when their computers go crazy again.

"You were warned." The face of Cadmus appears on their screens again. "The alien invaders are dangerous. Their intentions, malicious. They possess power we cannot hope to match. And their technology, brought from other worlds, is falling into the wrong hands. We should not be opening our arms to them. We should be locking them up and taking their weapon away. You did not heed us, but you will need the chaos that amnesty has brought. You will pay the price in fear and blood. And you will beg us to save you. We are Cadmus." They say before the screens go back to normal.

"I'm already getting sick of these guys." Peter tells the rest of them.

"Kind of a coincidence that Cadmus releases a new video just as criminals get their hands on alien weapons." Alex comments.

"What do Cadmus is the one giving the the weapons?" Kara asks.

"Then I'd like to know what idiot's in charge over there." Peter states but sees her point.

"So because the photon cannon is powered by electromagnetism, it left a radiation signature on Supergirl and Spider-Man's suits after the blasts, so we might be able to put a tracking algorithm together to find them." Winn says to Peter when they both see Alex is spaces out.

"Hey, you okay, Alex?" Peter asks.

"Maggie is such a terrible pool player. I even tried to let her win and she couldn't keep up." Alex tells them.

"Ma...Maggie, the NCPD Officer?" Winn asks.

"Yeah, she's been kind of down. Her girlfriend broke up with her." Alex explains.

"Must be tough." Peter replies to that news.

"I don't know, lately she just haven't been acting like...Maggie. She's normally so tough, and now she just seems vulnerable. I wish there was something I could do to help her." Alex explains.

"Yeah, I try to stay out of other people's relationships." Winn tells them.

"I wouldn't know, I'm the one to stay out of them as well. I'm engaged after all, I've got my own problems. Like trying to pick a date." Peter says when they get a alert of another attack.

"Attack at Jefferson and Park." Gwen calls from the labs and Peter runs off and takes to the sky.

-

Kara and Peter make it to see they have the weapons and are using them to make things float,

"You made it." One of them say and Peter uses his webs to web their car and they fight them off when the one with the antigravity gun shoots a police car, sending it into the air.

Kara flies off after it to save the officer and while he was distracted, Peter blasted their weapons but ended up getting run over by their secondary vehicle and escaped.

-

They return to the DEO and Peter has an ice pack to his head after that ramming he took.

"How's your head?" Gwen asks him.

"I have a thick skull, I'll live." Peter tells her, happy to have heard that Kara was able to save the cop at least.

"...you will beg us to save you. We are Cadmus." The video says as Winn looks over it for any clues.

"You are lame." Winn mocks holding a Nerf gun to the computer screen.

Peter and Gwen just chuckle at him loving having Winn around.

"You liking your new bestie?" Peter asks Gwen.

"Well, it is a bit boring being the only head of science, having someone who knows what they're doing and what you're saying helps. You know, someone I'm not dating and marrying." Gwen tells him.

"Yeah, we still need to pick a date." Peter tells her.

"I know, but I wanna find a perfect dress first before finding the perfect date for our perfect day." She tells him before kissing Peter.

-

The next day, Kara shows up saying Lena Luthor has asked Kara to have Supergirl protect her fundraiser from the people with the weapons. The bad news is that she also expects Kara to be there.

That's where Peter comes in.

"No. I'm not doing it." Peter states to her crazy plan.

"Come on, I just need you to use that hologram thing to make it seem that Supergirl is there while I'm there as Kara." Kara explains to him.

"You want me to be Supergirl for a whole night. For the sister of the madman that once tried to kill me." Peter informs her but sees she needs to keep her identity a secret and then decided to help her and activates the hologram and he gets replaced by Supergirl.

"How do I look?" Peter asks in Kara's voice.

"My god, the resemblance is uncanny." Kara comments on the device hearing her own voice coming from Peter.

-

Kara and Winn go to the party and meet up with Lena when Peter comes flying in with his hologram over so he's Supergirl.

"Supergirl. I'm glad you could make it." Lena tells him.

"Happy to help wherever I can." Peter says, trying his best to act like Kara. "But I still think this could be a bad idea."

"Well, why don't we wait and see how the evening pans out?" Lena replies to that.

"Kara, good to see you." Peter calls out to her. "I'll check the perimeter, and be back at the first sign of danger." He says before taking off.

The party goes on for a while until it gets interrupted by the gang appearing.

"My, my...look how many pretty things there are." The leader says.

"Oh, you picked the wrong party to crash." Lena tells them.

"I don't think so, princess." He replies when Peter comes flying in and lands ready to fight.

"Did you really think that I wouldn't be here?" Peter asks.

"Actually, I was counting on it." The leader replies before trying to shoot him but Peter was able to dodge it thanks to his senses and he puts a finger to his head to activate his laser vision coming from his lenses to make it look like they came from his eyes to not give him away and blasts their weapon but gets hit by another.

Underneath the banquet table, Lena was working on a device to shut down their weapons and Winn finds her and gives her an hand while Peter is fighting them all off as best as he can as Supergirl.

He holds on as long as he can when the weapons fly off into the air before exploding leaving them powerless.

"You ready to give up?" Peter asks them seeing they won.

-

During the transporting of the gang members, they all drop dead because of Lena's mother, Lillian who happens to be the leader of Cadmus.