It's been two weeks since Team Flash has defeated Multiplex but a new threat rises. The Darbinyan Crime Family are sitting down for dinner Araz Darbinyan starts talking about the future of the family business but then a green toxic mist enters the room slowly infecting their lungs and killing them all.

"Barry, come on get up..." Caitlin said slowly kissing his chest and neck.

"Ugh, what time is it?" Barry groaned rolling on his side.

Buzzz! Buzzz! Buzzz!

"Oh, come on!" Barry said groaning and Caitlin giggles.

He answers his phone.

"Hey, Joe, Oh, crap. I'm on my way. He said than gets dressed and kisses Caitlin goodbye. He heads to work in a rush.

"We've got multiple homicides," Joe said to Barry as he walked into the scene of the crime.

"Joe, I got the security tapes, and look," Eddie said walking towards Joe and Barry the tapes showing green gas choking the crime family.

"Joe, I'm gonna go to S.T.A.R. Labs," Barry said.

"Wait. Barry! I need to tell you that I'm reopening the case of your mother's murder," Joe whispers in his ear. Barry nodded and left.

"Hey, Beautiful," Barry said lovingly kissing his girlfriend.

"Hey, Handsome," Caitlin said.

"Guys, I think we've got a Meta-Human alert. He can control poisonous gas and I brought a tissue sample from the victims," Barry said. "I also think we're gonna have to find a place to store these Meta-Humans Iron Heights doesn't have the facilities to imprison them."

"There's one place that might hold them," Cisco commented.

"What are you talking about?"
Barry asked.

"The Particle Accelerator. It could be modified to act as a sort of makeshift prison." Dr. Wells said thoughtfully.

Sophia's face paled and she looked away from Wells, staring resolutely at the floor as memories that always came with that word flooded through her like a tsunami. Barry watched in concern of his sister, feeling pained at how miserable she looked.

~ Flashback ~

"Tonight, the future begins the work my team and I will do here will change our understanding of physics, will bring about advancements in power, advancements in medicine, and trust me, that the future will be here faster than you think," Dr. Wells said.

"Dr. Wells we just got the latest weather report a big thunderstorm is rolling in," Cisco informed.

"We're not launching a space shuttle
We'll be fine." Dr. Wells said.

"Tahiti?" Ronnie said.

"I know. It's a long flight but we can binge-watch our favorite shows while we wait," Sophia said.

"But what about Italy? Pizza and
wine and more Pizza." Ronnie pouted adorably.

"Yes, but Italy doesn't have Mai Tais and a Honeymoon isn't a Honeymoon without Mai Tais," Sophia said and kisses Ronnie.

"Dr. Wells the Accelerator is primed and ready for Particle injection," Cisco said beaming.

"Well, I feel I should say something profound like one small step for man but all I can think of to say is... I feel like I've waited for this day for centuries," Dr. Wells said.

"That's it? You'd think there be like
a loud bang." Cisco said.

"If there was a loud bang we'd all be in big trouble," Ronnie said.

"Take it from the guy who helped build it," Sophia said smiling at him.

"Ladies and Gentlemen... We did it!"
Scientists cheer and applauded. Then Alarm blaring and explosion booms.

~ End of Flashback ~

Dr. Wells had to say her name 3 times before she looked over. "Did you hear me? We're going down to the Accelerator ring."

Barry saved her from responding. "Actually, Dr. Wells. I could use Sophie's help in identifying the poison gas." She gave him a look of mixed thanks, relief, and he returned it with a small smile.

"Okay." He nods.

Cisco, Caitlin, and Dr. Wells entered the pipeline "This will definitely work. I need to check on something." Dr. Wells said and wheels out.

Caitlin then looks over to her friend.

"You okay?" She asks worriedly.

"Yeah, I was just remembering that day. I feel responsible for Ronnie's death. I could have saved him. He would still be here alive."

"Cisco, if he didn't a lot of people would have died. He made a sacrifice. I know how it feels. The guilt for all the lives lost because of our stupid mistake but he was a hero and he will never be forgotten."

Cisco nods and they hug tightly.

~ CCPD ~

Both siblings walk towards the main room.

"Allen!" The Captain walks towards him and then sees her.

"Sophia!" The Captain said hugging her.

"Captain Singh!" Sophia said hugging back.

"Haven't I told you to call me David young lady?"

"Sorry I forget sometimes."

"No worries. So, how are you doing?"
He asks.

"Great! I'm just here to help out Barry with a case."

"You're welcome to anytime. Anything for my favorite Allen," David said. Barry rolled his eyes.

"So, Barry. Where the heck is the review for the Olaf Case?"

"Upstairs," Barry said. Singh gave him an incredulous look.

"I-It's all finished... I can just run up and bring it down." He glanced at Sophia, then ran towards the stairs

"With you that could be three days from now; I'll go with you." Sophia chuckled and followed Barry

Once in Barry's lab, the forensic scientist handed the file over to his boss, then shared an amused look with Sophia.

"Clean up your lab, Barry. It's a mess. Also, tell Caitlin that I said hello." The Captain said.

"Oh, and keep Barry in check." The Captain said to Sophia.

"Will do, David. But Caitlin already has him whipped," Sophia said with a smirk making the Captain Laugh.

"Bye, Sophia." He leaves waving goodbye.

"Bye, David." She waves back.

"He was always your favorite," said Barry

"I can't help it if he likes me more than you."

He shakes his head smiling slightly.

"Come on let's get to work."

While they worked they were loud.
Laughter was heard inside Barry's Lab with music playing in the background.

"Can I ask you something?" Barry asks.

"Shoot."

"Are you okay? I know it's a dumb question but I saw your face it looked like you saw a ghost. Was it about Ronnie?"

"Yeah, it's just he wasn't supposed to be there that night. He was there just for me. I just miss him a lot. We've ruined people's lives, Barry. We can't fix that." Sophia said her voice cracking.

"Hey, come here. It's okay," Barry said and soothes his sister.

The computer then beeps alerting them.

"This is weird. It seems that there were two different strands of DNA in the victim's lungs?" Sophia said.

"How can another person's DNA get inside the victim's lungs?" Barry asked confused.

"What if the Meta we're looking for doesn't control gas but becomes it?"
Barry said.

"All available units we have a report of a toxic gas attack in the Central City Shopping Mall." A police dispatcher said through the radio.

Barry got up to leave.

"Barry, you can't we don't even know what we're facing yet it's not safe." Sophia pleaded.

"Sophie, I have to go," Barry said kissing her forehead.

A woman is in an elevator and just as the doors are about to close a man walks in. "Jude Howard it's nice to see you again."

"I thought you died."

"You say that like it was an accident."

"You remember the last thing you
said to me in the courtroom?"

"May God have mercy on your soul."
The man then turns into green toxic gas and kills her.

Barry speeds to the mall where he finds the woman already dead in the corner of his eye he sees gas go through a door he follows it to a narrow corridor where the gas turns back into a man.

"Why did you kill that woman!?"

"She deserved to die!"

"Now, go run away. I still have one more name on my list. Don't make me
add you to it too."

They start to fight but Barry is
no match and is poisoned.

"Barry, can you hear me?" Caitlin yelled over the coms.

"His vitals are weak but he's alive, Caitlin, I'm sure he's fine." Cisco pointed out, much more calmly.

As if on cue, Barry rushed into the room, coughing and spluttering. "I can't breathe." He managed, gasping in rough breaths of air.

"He needs oxygen!" Dr. Wells said.

Sophia arrives.

"Barry! Oh my god! What happened!" Sophia yelled as the Flash was thrown onto a bed, Cisco running a special medical tool over his chest.

"The Meta poisoned him," Cisco replied

"Barry, you're going to be okay. I've got you." Caitlin said calmly.

"Cut him open the poison's still inside him." Said Sophia.

"He brought us a sample." Dr. Wells said, his face serious. "Caitlin, we need to do a pulmonary biopsy; extract an active portion of that gas."

"Cisco, give me the syringe" Caitlin ordered.

"It's a small needle you probably won't even feel it," Cisco said sarcastically.

"You're are definitely going to feel it," Caitlin said before stabbing him in the chest.

"Ahhh!" Barry screamed.

~ Later ~

Monitor beeping steadily.

"The streak lives." Cisco's grinning face came into view, and Barry offered him a weak smile in return.

"You'd be dead if your lung cells didn't regenerate so quickly." Caitlin's face was drawn and tired, and she looked scared.

He held her hand and squeeze it gently rubbing circles on her palm relaxing her.

"Ahh... my chest feels like that one time I had a cigarette." Barry sat up slightly. Caitlin gave him a grin.

"Yeah, well, you only did it because Cisco dared you at Ronnie's Birthday Party," Caitlin added.

"Hey, it's not my fault Barry wanted to impress you," Cisco said.

"Aww, I'm flattered," Caitlin said and kisses his cheek. Barry looks embarrassed.

"We were wild back then. Good times." Cisco reminisced. Caitlin and Barry chuckled.

"This isn't funny!" Sophia snapped. "You could have died!"

"I didn't," Barry said.

"Now that we have a sample, we'll get to work analyzing it, figure out the makeup of the poison, maybe get a clue as to his human identity." Dr. Wells said.

"Or at least a way to stop him from turning into a mist, The Mist okay that's his name end of discussion." Cisco grinned.

"I have to get to the Station."

"You should be resting." Sophia and Caitlin said in unison.

"I have to talk to Joe." He kissed Caitlin on the cheek and left.

~ Much Later ~

Sophia was sitting on the treadmill room.

"I sorry, Sophie. I didn't mean to scare you by leaving like that earlier.

"It's okay. I get it you had to go. It's just... that's the last thing that Ronnie said to me that night." She said sadly. He then sits next to her.

"You know I'm glad you two got together. I might have been overprotective at first but he made you smile and laugh even when sometimes I couldn't." Barry said.

"You know for so long, I've been terrified of going into that hole," Sophia said opening up.

"I'll go with you," Barry said grabbing her hand.

When they arrived, Sophia was overwhelmed by memories of her
and Ronnie.

She felt tears prick at her eyes.

"No one will even know how much of a hero he was that night. First Mom and now Ronnie. Why do the people I love always die?"

Barry wrapped his arms around Sophia and pulled her into a hug.

"It's okay, sis. Listen this is not your fault. You can't let the bad ruin the good. I'm still here and I'm never gonna leave you."

Cisco's voice came through the intercom.

"Hey, you guys down there? You
need to get up here ASAP!"

"You told us that this guy had one more victim to go so we looked for who caught him it was Joe," Cisco said.

"Wait before you go I reversed engineered this antidote from the toxin I hope you don't have to use it," Caitlin said kissing him on the cheek.

Barry picked up his phone and dialed Eddie Thawne.

"Hey, Eddie. Do you know where
Joe went?" He asks.

"He went to Iron Heights to see
your Dad." He answered.

~ Iron Heights ~

Joe is talking to Henry Allen about reopening Nora Allen's case. Suddenly The Mist arrives and starts to poison Joe but Barry arrives just in time and gives Joe the antidote.

"You need to stay away from him. Barry Don't breathe him in." Sophia warned.

"You can't fight him, Barry! Just keep him coming at you that should sap his strength." Caitlin said.

"Gas is the least stable form of matter. This meta-human will not be able to stay in his mist form for long his particles will need to reform." Dr. Wells said.

"Barry! Barry?" Dr.Wells asked.

"We win," Barry told them.  Everyone who was on edge relaxed.

Once Barry had returned to S.T.A.R. Labs Caitlin Pushed herself off her chair and ran into his arms. She wrapped her arms around him and buried her head in his neck. Feeling the warmth radiate from his body she let out a sigh of relief before loosening her grip. Barry planted a kiss on her lips.

"I'm okay," He said.

"I know. I was just really scared."

"Well, I'm here safe and sound in your arms, Snowflake"

"Good job, Bartholomew," Sophia
said teasing him. Barry groans.

"Group hug," said Cisco.

Barry's stomach then growls.

"Come on let's get some food. I'm starving." He said rubbing his stomach.