Hey guys, this is a new story because I like how Oliver and Barry interact with each other and I honestly ship this two together. In this story, Barry is a female and I add Sebastian inside because why not.

Pairing: Oliver/Fem Barry, Eddie/Iris

Crossover: Arrow/Flash

Isabella "Bella" Allen and her brother Sebastian James Allen are identical twins who are competitive with each other growing up. Until they are 11 years old, they have a fall out because they disagree on the death of their mother. Isabella has seen her mother being murdered by a man in a yellow lightning but not her brother since he's at his friend's house for a sleepover. The only two people who believe her are her dad and Iris. She thought that her own brother would believe her but she had called their dad a murderer and it broke both hers and their dad's hearts. She has been sent to every therapist and counselor about what she saw is impossible but she wouldn't budge. Since her dad is being sent to jail, Joe, who is a cop and her dad's friend, adopted her to live with him and Iris. She and Iris became very close like sisters. Her brother was adopted by a family and he quickly changes his last name to Smythe and his foster family lives in Westerville, Ohio.

Berry and Iris have been best friends from childhood before Isabella's and Sebastian's' mom is murdered. They are joined at the hip until college. After they graduate, Berry joins the Central City Police Department and becomes an assistant forensic scientist, in another word is CSI, to investigate what happened to the victims at the crime scene and not only that to find out who killed her mom and bring justice to her dad.

A few days ago before the release of the Particle Accelerator, she goes to Starling City to check for impossible sightings. She has heard about the vigilante that saves the city so she thought that he could help him.

In Starling City, there was a break in at Queen Consolidate. An officer was at his night shift until a man came in, ripping the door with his bare hands and grabbed the guard and snapped his neck with one hand. After that, he grabbed what he came for and left. In the morning, Officer Lance(got demoted from detective to officer), Oliver, Diggle, and Felicity are looking at the crime scene with the other officers.

"This door was made of expanded reinforced titanium," Lance tells them

"What did they use to do this?" Oliver ask Lance

"Not sure yet. No sign of any explosives. Maybe a crane, maybe a forklift." Lance tells them as he points out the non-obvious clues

"I'm guessing there were at least three of them, maybe four." Diggle guess on the theory

"And given how quick they got in and out of here... They were fast." Oliver continue on the theory

A woman steps out of a train in Starling City. It is pouring and she is late since she misses the first train and the second is delayed. She grabs her luggage and hurries to the train station. As she saw her taxi, the taxi driver drove off leaving her.

"Whoa, hey, stop, wait! You don't even have a fare!" She called to the taxi driver before getting splash by a passing car.

" Any idea what these guys were so hot to break in here for?" Officer Lance ask Diggle

"You didn't happen to leave a spare earthquake machine lying around, did you?" Diggle sarcastically ask

"Sorry. This is what we're able to pull off the security cameras. He was the only guy we got on video. The rest of the crew must have come in after him." Lance tells Oliver, Diggle, and Felicity

"Actually, it was only one guy. Ah, sorry I'm late. But actually, my train was late. Well, the second one. The first one I did miss, but that was my cab driver's fault. I've got this great traffic app, and... But he thought that he was right. I'm here now, though" A woman comes in carrying a shoulder bag and strolling in with a metal suitcase. She's babbling on her tardiness.

"So. Great. Who the hell are you? And do your parents know that you're here?" Officer Lance ask her

" I'm Bella Allen. I'm from the Central City police department. I'm with the crime scene investigation unit" She took out her badge to show them

"We're working on a case with some similar unexplained elements in Central City, so when the report of your robbery came over the wire, my captain sent me up here." She tells them about her being here

" And you think one guy ripped through this door like it was tin foil?" Lance ask her

" One very strong guy, yeah. Uh, it takes about 1,250-foot pounds of torque to break someone's neck. You see the marks on the guard's neck? The bruising pattern suggests the killer used only one hand." She explains to the group and she stares at Oliver

" I'm guessing you don't know how hard it is to break someone's neck," Berry ask Oliver who is staring at the victim's neck

" Hmm? No. No idea" Oliver broke out of trance and answer her

" Uh, we're going to need a list of the entire inventory here to figure out exactly what was stolen." Lance starts to order the other officers

"Actually, I think I know what was stolen. A centrifuge. An industrial centrifuge. Probably the Kord Enterprises 2BX 900. Maybe the six series. Both have a three column base. Here, you can see the three sets of broken bolts where the thief just... ripped it out of the ground." Bella tells them what and how is it stolen

" And what exactly is a centrifuge?" Lance ask

" It separates liquids." Bella starts to explain when Felicity interrupts

"The centripetal acceleration causes denser substances to separate out along the radial direction. And lighter objects move to the top. What did you say your name was again?" Felicity explains and asks Bella

"Bella. Allen." She introduce herself

"Felicity. Smoak." Felicity introduce back

"Um, you can see the cracks heading towards the door. Footsteps. One guy. Anyway, it's just a theory. One backed by a lot of evidence." Bella continuing her explanation

"There has to be another explanation," Lance argue

"Yeah. I'm sure you're right." Bella looking down

"You might want to fill our mutual friend in on this," Lance tells Diggle

"Yeah. Don't worry. I'm sure he's already on it." Diggle already knows that Oliver knows about the issue

*Oliver's flashback*

"We need to change directions 10 degrees north," Sara tells the other while Slade starts to groan

"We need to rest," Shado argues to Sara

"If Ivo and any of his men survived that blast, they'll be tracking us. We keep moving." Sara argues back

"Five minutes. You watch him, please?" Shado tells Sara before asking Oliver to watch Slade while Slade groans

"Of course," Oliver answer her

"Do you believe them? That this Hosen will lead us to a wrecked Japanese sub?" Shado ask Oliver

"Ivo seems to think so. I just hope whatever miracle serum they're after is actually onboard. For his sake." He hopes about the serum helping his friend

"How do you know that girl?" Shado ask Oliver

"Sara was on my father's boat... with me," Oliver tells her the truth

"What about the girl in the picture? Laurel? The girl you told me you were in love with." She ask some more

"Sara is her sister." Oliver truthfully answer and Slade starts to groan

"I feel like taking a walk. Anyone care to join me?"

"I guess a lot's happened in the last year," Oliver says before starting to walk with the rest of the group

*At Oliver's office in Queen Consolidate*

"Oliver. Got the final inventory from applied sciences. That CSI from Central City was right. The only thing missing is a centrifuge." Diggle explains to Oliver and Felicity walks in with a laptop on her hand

"You have to see this. I pulled up CC traffic camera footage from across the street of applied sciences. This is three minutes after the alarm went off." A video shows a man carrying the centrifuge with one hand and place in the truck before driving away.

"Can we help you with something, Detective?" Oliver ask as he sees Bella coming towards them.

"Oh, CSIs aren't actually detectives. We don't even carry guns. Just some plastic baggies." Felicity laughs at the joke and so does Bella

"Uh, where should I set up my equipment?" Bella ask them

" I'll show you." Felicity helps Bella

"What's going on?" Oliver ask

"Your assistant said that you preferred to keep the investigation in-house, so I cleared it with my captain to give you a hand," Bella explains to him and Oliver pulls Felicity aside to talk to her

"What are you doing?" Oliver ask Felicity

" We need to find this intruder. And she seems to know more about it than any of us. Forensic science isn't exactly my forte, so... I'd say we need her. Wouldn't you?" Felicity convince Oliver

"Mm-hmm." Oliver agree and Felicity walks away from him

" I'll show you around." She shows Bella out of the office and follows her out

"Why am I getting the feeling you know more about this than Felicity's new friend?" Diggle ask Oliver as Bella and Felicity left the room

"Pray, I'm wrong," Oliver tells him

Next one will be tomorrow because I'm almost done editing it and I can publish it. Please review so I can continue.