Author's Side-Note: Warning, this chapter may go dark at some points and involves a fair amount of swearing. You have been warned.

To say that Caitlin wasn't training a lot after Team Flash's unexpected encounter with Reverse Flash during the Christmas period would have been completely wrong: because ever since that day, Caitlin had been increasing her training in an attempt to both get faster, and to get stronger too, and both reasons were simple: so she could defeat Reverse Flash the next time the two of them fought one another!

In fact, the only one who managed to keep her from exhausting herself out most of the time was Barry, and that was because he was tasked with keeping an eye on her vitals during the training sessions...well, that and because he cared about Caitlin, of course. But Caitlin wasn't the only one who was going a little overboard...

What the others didn't know, or at least that's he hoped anyway, was that Barry was running blood tests on himself whenever he had been alone, and had also been tinkering around on something as well when Cisco and Caitlin weren't around, which wasn't as often as you'd think unless they were teaming up to work together since Caitlin often went out on her own.

The tests varied as each day went by, but Barry always strangely got the same result each and every time: absolutely nothing. Whenever he tried and went out for a few minutes to top up on Jitters' coffee and savory goods: the tests would always say that there was no results to them, yet when Barry investigated further into the matter he would always find that someone had tampered with the results and erased the results, leading him nowhere!

And as much as he would try to figure out who or what could have done it, he was left with even less clues and suspects than when he started with for a few good reasons:

1. He had told nobody about these tests so as to not worry anyone, especially Caitlin given how hard she was pushing herself lately.

2. He always hid his tracks whenever he left S.T.A.R. Labs and the tests were going on in case someone like Caitlin, Cisco or Dr. Wells came in and discovered it.

And 3. He trusted everyone at S.T.A.R. Labs with his life, that included Joe whenever he came to S.T.A.R. Labs with a case or to check on everyone.

Unfortunately that also meant that someone must have sneaked in and found a way to access the results before sabotaging them, but who was as much of a mystery as anything...It was then that he sighed in frustration after the same thing happened for the third straight week in a row that he realized what he had to do: he needed help to figure out about the results without them being sabotaged...and he needed to tell someone about why he was doing the tests...more specifically: he needed to tell his friends, Caitlin and Cisco!

That evening after work had finished up: Barry asked both Cisco and Caitlin to meet him at the bar to discuss the matter. Although Barry was a bit cryptic with his message, having said 'Need to talk about something, meet me at the bar.'

The aforementioned bar in particular was the one that the trio had gone to not too long after Barry's return, during the time when all three of them decided to let loose and enjoy a break whilst rekindling and hanging out for old times sake. It was as good of a place for good memories as any.

They arrived not too long afterwards, and they saw a rather stressed looking Barry sitting at the bar with a drink in hand, even if they knew it wouldn't affect him due to his powers. Caitlin was the first to inquire about Barry.

"Barry? Are you okay?" He sighed and slowly shrugged his shoulders. "I've...been better...there's something I need to tell you guys." he began, which got Cisco and Cait a little worried. "What's up dude?" Cisco then asked as his and Caitlin's drinks came to them, and the three sat at a table away from the bar. Barry took a deep breath and slowly began to speak.

"Sooo...the last few weeks since...he appeared...I've been trying to run some tests...on myself...and I think you both know the reason why?" they both nodded slowly, not in confusion but in an uncomfortable way of remembering the few times that Killer Frost had appeared. Needless to say, Barry's frozen alter ego wasn't their cup of tea, for lack of better terms.

"So this is why you keep locking your computer when you leave for a bit." Cisco remarked with a cheeky smirk on his face, which earned him an unimpressed side-ways glance from Barry and an eye roll from Caitlin. Caitlin, however, had quickly read between the lines with what Barry had already said.

"You said you've been trying to run the tests for a few weeks? Did something happen?" she asked her meta-human boyfriend, and he nodded slowly as he turned to look at them both. "Before I continue: understand that I know you two weren't responsible for what I'm about to say. And I know that because I trust you two more than anything."

That both warmed their hearts and made them a little concerned at the same time, as now they were concerned on the potential severity of this problem as Barry began to explain. "Every time I've tried to do these tests and I've gone out for whatever reason, I've always locked the computer to protect the data. And yet, whenever I return for the results, I find that the data has been deleted by someone accessing it, and has managed to lose all the data."

This seemed to make Caitlin and Cisco concerned...but Caitlin slowly placed one of her hands on Barry's before asking softly "What do you need from us, Barry?" He managed a small smile at Caitlin for her understanding, even if it was briefly until returning to seriousness.

"I...need help in figuring Savitar out, figuring me out...and I don't think I can do it S.T.A.R. Labs with some mystery person who seems to have access to our files tampering with the work...So, I guess I'm asking...do you two think you can help me without getting Dr. Wells or anyone else involved...?" They took a moment to think on that, but both scientists quickly thought of something...or I should say "someone".

"Weeelll...I think we both know a few people outside of Central City who might be willing to do us another favor." Cisco began with a knowing look on his face, something that Caitlin understood because she had the same thought in mind...but also one that also confused Barry, since he was the only one that was not in the know. "Who?" he asked confused. Caitlin and Cisco both replied with a smirk on their faces. ""Oliver Queen.""

Contrary to belief: Oliver Queen had known the three scientists for a long, long time now since the days of them being at school together. Mostly from occasions when he had come to Central City with his parents on a few occasions on business trips...or as Oliver and Thea had been told back then as "family holidays", despite knowing better.

They had also made friends with Felicity Smoak, Oliver's girlfriend, during their school years, with Caitlin and Felicity becoming best friends when started visiting each other without the other knowing every-so-often over the years. This was after they became pen pales though after one of Barry's performances in school that she had visited.

After Barry moved to Star City University though: Oliver, Felicity and Barry grew even closer as friends, despite a rocky start, and Oliver even let Barry stay around his house during his time at Uni and brought him into Oliver's friendship circle as well: causing Barry to become friends with Laurel and Sara Lance, Laurel's boyfriend Tommy Merlyn, and Oliver's sister, Thea, as well.

They were memories of a really great time, despite the bad time Barry and Caitlin were both in at the time in their life after their argument...

Planning out the whole trip to Star City was not as easy as it seemed, due in no small part due to their jobs in S.T.A.R. Labs and Caitlin's work as The Flash. Fortunately though, they managed to gain a reprieve from the chaos, strangely, a few days after Barry's chat with Cait and Cisco in the bar.

Dr. Wells was currently going away on a treat for a few days, though what for they neither knew nor did he say, and lately meta-human attacks had been between low and non-existent. So, the trio decided that those few days would be the perfect time to go to Star City to get help with Barry's "Killer Frost Crisis", as Cisco had dubbed. Why and for what reason? Only Cisco knew, naturally.

They made sure they had a meta-human alert installed into their phones just in case, just in case Cisco needed to breech them there and there was a crisis going on, and the West family had been told in advance that they were going away for a few days. Joe was, naturally, the only one who had a clue why because of his years of detecting...well, that and he revealed to the team once that Barry mumbled it in his sleep, much to everyone but Barry's amusement, but details!

Present Day - Star City:

Currently, on one of many rooftops over-looking the vast landscape of buildings and busy streets of Star City, the local vigilante of Star City, aka "The Arrow", stood atop the roof of a building that happened to be where his base was and where he was supposed to be meeting a certain trio of meta-humans who had each made their mark on history in Central City.

He hadn't been there long, but it was long enough to get bored without letting his trigger-fingers going for an arrow to fire. It was a force of habit that he hadn't been able to break, nor did he even try to break when being 'The Vigilante', as he was dubbed by the people of his city.

Thankfully for his sanity's sake though...or what little remained of it anyway...he didn't have to wait too much longer, as moments later he heard a breech portal opening up behind him. He didn't even need to turn around to see who or what it was at this point, as he had seen this a few times in the past to now.

"You're late!" The Arrow spoke to his new visitors, and finally began to turn to face them, only to receive a shock when he saw who stood there before him. "Never stopped you in the past, huh Oliver?" There stood in front of Star City's vigilante was not only 2 meta-humans he respected, but the face of a friend he had not seen in years, bringing a rare genuine smile to the vigilantes face.

"Barry Allen...you son of bitch, you're alive!" The revealed Oliver Queen said as he walked over to Barry and pulled the meta-human into a single-arm bro hug, one that Barry responded to immediately with a small laugh, and brought a small smile to Caitlin and Cisco's faces. When the two friends parted from their hug shortly after starting it, Oliver playfully smacked Barry around the back of his head, causing the latter person to rub the back of his head.

"You have a lot of explaining to do, and not just to me." Oliver said with a smirk, and Barry rolled his eyes at that a bit. Star City's vigilante then looked over to Central Cities two heroes. "Good to see you two again, Vibe and Flash." Arrow said, which they smiled back and nodded in response.

When they eventually got to Oliver's base of operations: Felicity, Thea and Sara all brought their long lost friend into a tight hug one-after-the-other after hugging Caitlin and Cisco...and naturally Barry got punched in the arm by Felicity for not saying sooner that he was back, which the others in the room laughed at a bit.

"What happened to you!? We all thought you were dead!" Thea spoke, and Barry rubbed the back of his neck slowly, speaking a little nervously as he looked to the 4 friends in the room. "That's...actually a reason why I'm here..." he began, before being interrupted by a voice entering the room saying "Sounds ominous. Friend of yours Oliver?"

The voice belonged to Oliver's bodyguard, and arguably The Arrow's longest standing ally before Felicity joined the team: John Diggle. He was also followed by a fairly young guy in a red hoodie jacket who looked closer to Thea's age than anyone else's age. It was the former of the two who spoke. Oliver introduced the two of them to Barry.

"John, you remember Caitlin and Cisco from Central City. This guy here is an old friend of ours: Barry Allen. Barry Allen, these two are my bodyguard and Thea's boyfriend: John Diggle and Roy Harper. They work with me as well as the others."

Barry shook the hands of both men, though he was a little surprised by the grip Roy had, and both were surprised by how cold Barry felt. Diggle was the first to speak up. "Pleasure. Oliver spoke a lot about you." That caused Barry to look at Oliver with a raised eyebrow as Diggle and Roy looked to Caitlin and Cisco. "Good to see you two again, Vibe and Flash." Diggle said, using their aliases in this case.

Barry soon began to explain everything that had happened: from his "death" at the hands of Reverse Flash, though mentioning that he hadn't known that until recently alongside Caitlin and Cisco, to spending years hiding in the shadows and causing chaos as Killer Frost, and to Caitlin bringing him back from Killer Frost's icy hold, pun very much intended.

Caitlin and Cisco helped explain it along the way with what they knew, though Caitlin spoke more often than not when she felt she needed to, but the results were still the same: Team Arrow's faces were a mixture of surprise or disbelief at what Barry had been through. When Barry got to the main topic at hand though, that was were things started to get interesting.

"So, let me just wrap my head around this..." Felicity began after Barry explained his current situation with the blood test fiasco, trying to process everything at once. "Sooo, you're saying that somebody has been managing to sabotage your test results and somehow hack into your computer, and none of you know who it could be? And you need us to help figure it out? Am I rambling, I think I'm rambling..."

Barry nodded slowly, though not at the "rambling" part. "Yeah...can you help me? Even if...even if it means...talking to...him...?" By 'him', he was referring to the very alter ego that he was trying to figure out, that he had been trying to figure out for far too long now...Killer Frost.

Everyone looked towards one another, nobody daring to speak for a long time, until eventually Oliver nodded to that. "Okay." was all he said...though he was going to wish that he hadn't agreed sooner or later....

Barry was eventually sat down on a chair in the base, a few strange wires and contraptions attached to his head or fingers to monitor him carefully. Caitlin stood next to Barry as Felicity took a sample of his blood for analysis. Caitlin though was a concerned for her boyfriend, and not just for the test results: when Barry had sat down on the chair, he had insisted on being strapped down to at least try to prevent himself from getting free in the event that "he" took control, despite his power-dampening necklace still being on at the time.

"You okay, Barry?" she asked softly, slowly placing a hand on his shoulder for some measure of comfort. He slowly shook his head no. "I'd be lying if I said I was...or that I'm not scared." She gently squeezed his shoulder for comfort, and gave him a soft kiss on the cheek, much to the surprise of some in the room who were watching, before whispering to him. "Well, I'm here for you, and I'm not going away. We all are. I promise."

He took a breath as his eyes briefly closed...then he said something that surprised everyone. "There's...something else. Something I didn't mention, to anyone...Something about Savitar." That made Caitlin and Cisco concerned, especially given that Barry was about to mention something about his icy alter ego that seemed to be scaring even him. Scaring him enough that he hadn't mentioned something till now.

"Savitar?" Roy asked, a little confused, before Cisco clarified for him. "That's the name that Barry and Caitlin have for Killer Frost, his alter ego." Caitlin knelled down next to Barry as she listened to what he had to say, everyone else also listened closely as well for what he had to say.

"He knows. He knows everything. Everything we've been through, everything that has happened or that is likely to happen...even things that I still don't know, like who Reverse Flash really is. And...And I think he's known about it for a long time now. And every time I try to figure it out...he wipes the memory clean from my mind, or locks it away in his so that I don't know it...and it terrifies me to know that he knows so much, and I can't figure it out! Or that he can simply manipulate what knowledge I can found out from him like a switch!"

Needless to say, that sent a noticeable chill down everyone's spines, all the way down to their cores, even if some would never admit it like Oliver. Felicity soon slowly looked over and spoke something that terrified Barry, if only a little bit visibly. "I...I need to take a sample of his blood as well...Just in case there is any differences." Barry's hand clenched and opened up again every-so-often, and he had to close his eyes to calm down a bit.

"You don't have to do this if you don't want to Barry." Oliver said, saying what was on Caitlin's mind before she could voice it. Barry slowly shook his head. "I need to know..." he said, before opening his eyes and looking towards the others, his eyes radiating fear...but also unwavering conviction and determination. He may not have wanted this, but he wasn't about to stop now. That was the kind of man he was.

"Just, promise me one thing." he said, looking directly at Caitlin as he said that, to which she nodded frantically. "Anything." she said. "Bring me back when you figured out what he wants, or figured out anything." Caitlin slowly nodded to her boyfriends request, even though a part of her didn't want to in fear of losing the man she loved. She slowly stood up and kissed him on the lips briefly before pulling away and took the necklace off as Barry closed his eyes, waiting for the inevitable to happen...and the inevitable happened far quicker than anyone thought it would do.

As soon as the necklace was removed, the atmosphere of the room began to get colder, harsher almost, and Barry's skin began to go the deathly pale shade that was now known with Killer Frost, then the scars came quickly after, the change in the colour of his hair...and with one loud gasp his eyes opened: revealing the eyes that help identify him from Barry. Killer Frost was now in control!

The change had been so sudden that Team Arrow didn't know what to make of it at first. But they all agreed on one thing mentally: the transformation was terrifying!

For the longest time, Killer Frost never spoke a word, nor did anyone else: he simply glanced between Caitlin to everyone else in the room, then at his new surroundings, all with an emotionless scowl on his face. When he did speak, it sent another chill down the spines of Barry's friends.

"Hello there...puny, little insects..." he glanced at Caitlin briefly. "Flash...still alive I see..." his tone seemed to be a little less threatening towards her than normal, but his words still were laced with icy venom and hatred with every word spoken. Nobody spoke still though. "Not going to talk? Or do I have to sit here waiting for this blood test Barry's been trying to do for weeks?"

"You knew?" Felicity soon asked, causing the icy alter ego of Barry Allen to turn his head towards her to acknowledge what she had said, and to see her. "I know many things, Miss Smoak." he turned his head back to the others and continued. "Oh don't look so surprised. That little necklace blocks me out, sure, but I can still easily read his thoughts and memories like an open book...it's actually quite amusing to know that I terrify my other half!"

To say that he wasn't getting under the skin of everyone already would be incorrect, because he already was. Caitlin was the only one who wasn't letting him after her that much, quite possibly because of the good inside him: Barry. Felicity took the blood from Frost, though he didn't even flinch at all during the process: he just stared without emotion towards the people in front of him...until a coy smirk appeared on his face.

"As far as "interrogations" go: this is a very dull and non-existent one. And here I was hoping I'd have some "fun" through this. Ah well..." his face molded into a serious look again, and he gripped onto the chair as his powers began to freeze both the chair and the bounds keeping him restrained in seconds, before he smashed out of them and stood upright in front of everyone!

Diggle, Sara and Oliver, on instinct alone, ended up pointing their weapons at Killer Frost, only for Caitlin and Cisco to get in front of them and Killer Frost to stop them. ""Don't!"" they both said, but Frost just encouraged it with a snarl of rage on his face. "No...go ahead! You kill me, you kill Barry, that's how this works! I sure as hell don't have problem dragging him with me five feet under, so COME ON! DO IT!!!"

Silence. That's all that came afterwards. Nothing but the silence from every person in that room. At least for a time....

"Diggle, Sara. Put the guns down." Oliver said as he slowly lowered his bow. Diggle and Sara would do the same with their respective guns moments later, and Killer Frost slowly began to smirk, if only very briefly. He slowly walked over to a nearby wall and leaned against it, crossing his arms across his chest, waiting for it to begin. Caitlin spoke first.

"Why did you save me from Reverse Flash back in December?" Killer Frost showed no emotion to that question, at least not outwardly, but he still took his time to respond. "Because Barry cares about you. As much as I may not like you, he does...and besides, we share a common enemy in Reverse Flash..."

"Why would you hate Reverse Flash though? I mean, you're both killers and let you go on your killing spree." Diggle asked, his hands still on the gun he had at his side, asking a question that was on the minds of the others...but that turned out to be the wrong question to ask, and the wrong thing to say, as it seemed to strike a nerve with the icy meta-human as he stood up straight and glared at them all with pure hate...almost like what Diggle said had offended him...

"You think that I enjoyed killing all those people? Well guess what...you're damn right I did, but that was because each and every single one of those people DESERVED it! You ever stop to wonder or figure out anything about my targets? Or why I targeted them in particular and not some homeless person lying in the streets, or a family in the park, at their home, or in the middle of the street!?"

If there was a way for Killer Frost to somehow become even more scarier and chilling, pun not intended this time, when he was pissed off: then they had just found out how. The anger that was radiating off of him was immense! And yet the more he spoke in anger, the more that Caitlin, Cisco and Oliver assumed that the anger wasn't just directed at them for their accusations....

"No, you don't think about it! You don't think about it all! Because if you did, if you all did, even for the minutest of seconds, you would come to understand that each and every single one of those people that I killed, in their offices, at their hotels, in the streets or in alley ways, HELL even in their homes when nobody was around...each and every one of those bastards DESERVED IT!

"They DESERVED what they had coming to them because they were the ones that were corrupt! They DESERVED what they had coming to them because they were the ones hiring killers and assassins like Malcolm Merlyn, or Deathstroke, or Ra's al Ghul and using them to kill their rivals, their competition, or the innocent, or silence those that knew too much! They all DESERVED it, because they were the filth that stained the world that The Flash, or The Arrow, could never touch or didn't know about because they acted like the picture perfect role models!"

His fists clenched, and soon icy mist began to radiate from it, his hate filled gaze burning into the souls and memories of the individuals in front of him as he continued.

"I'm not perfect, I realized that years ago! Neither is Barry, or ANY of you tiny, miserable little insects! I'm not doing this to try and win in this never-ending little "game", or because I want to make a name for myself! I don't give a crap about super heroes rushing about trying to stop me from killing people, or stopping the villains that pay little attention to cloaking themselves, or love making themselves known like Leonard Snart and Mick Rory! And I damn sure don't do this to be a "hero", because being the hero is boring!

"I do what I do because, for me, it's RIGHT! Because somebody needs to wipe out those who smear their filth across the world when nobody else, not even the "heroes", will do! And because, at the end of the day, it was FUN! Just as it will be fun to kill The Reverse Flash for what he did to me! For what he did to Barry! And...!" He stopped pacing as he stood in front of one person in particular, staring her right in the eyes with his eyes: Caitlin.

"And, most of all, for what he will do if he is allowed to live and rot in a cell..." he points a finger towards Caitlin. "And not you, Caitlin Snow, or Barry Allen..." He pointed his finger at the others in the room, all who were slightly terrified of Killer Frost now "...or any of you lot or your companions...is going to stop me...! One way or another: Reverse Flash WILL die by my hands!"

For a whole minute, nobody spoke and nothing could be heard but the sound of Killer Frost catching his breath...that was until he suddenly grabbed onto his head as a shooting pain shot throughout his entire body and he collapsed onto a knee in front of the others, grimacing in pain yet with a snarl of rage on his face at the same time, as he felt his grip and control slipping from Barry fighting back against his will.

"N-No...! I...I won't allow you...!" he tried to protest, but a swift punch to the jaw by Oliver caused Frost to lose control concentration, and simultaneously in the process allow Barry to regain control! Caitlin, who was by his side instantly, put the necklace back around his neck, allowing Barry to relax and gain control fully once again, before holding him close to her and kissing the side of his head a couple of times whilst whispering to him in his ear "You're okay...everything's okay..."

It took some time for Barry to mentally recovered, and the same applied to the others for what they had witnessed with Frost and everything he had said. Caitlin and Cisco sat next to their friend, with Caitlin laying his head on her shoulder whilst she had an arm around his waist, whilst Cisco had a hand on his pals shoulder. And it wasn't just to help calm him down. The two also did it to help them out as well at what the darker side of Barry was intent on doing if he ever got control fully again.

Eventually Felicity came over with both blood test results. Truth be told they had been done way before Killer Frost had broken out of the chair, but given what was going on at the time and the fact that Barry wasn't in the right mental state afterwards right away: Felicity and Oliver didn't think it was the right time and that they should wait.

"So...both blood tests came in and mental brain activity tests, and...well, take a look." Felicity said as she handed Barry her pad, which had both blood test results. Both DNA matches were completely the same, which to fair was expected, but when looking at it from another perspective there was some subtle differences. Killer Frost was, quite literally, cold blooded.

And with the brain activity: Killer Frost's was operating on a completely different wave length to Barry's, but was also working overtime at the same time, and spiked every time it connected with Barry's consciousness and thoughts. It might not have been what Barry needed, not entirely, but it did help him out.

"Barry, what are you going to do about him? You can't keep him at bay forever..." Felicity asked out of concern, to which Barry sighs as he rubs his hands across his face, honestly at a loss at what he was going to do. "Honestly...I have no idea..." he said, and there was genuine fear in his voice, and who could blame him?

"Hey, he won't take control Barry, I promise." Caitlin said as she took his hands in hers. "We're a team, a family, and we won't let him take control of you and your life again, I promise." Barry managed a small smile at that a bit, before Cisco and Oliver added in one-after-the-other.

"Caity's right man. I already lost my pal once, and there's no way that we're going to let that happen again." Cisco began, then Oliver followed by saying "They're right, Barry. And you've got us if you need a little extra help. No way am I going to let some frosty alter ego and a lunatic in yellow ruin my friends life."

Barry smiled at his friends a bit, and nodded slowly, hoping that they were right. "Thanks guys..." was all he said before they got up and left the hideout. That evening when they got back to the Queen compound: Oliver and Thea invited over their other friends like Laurel Lance, who hugged Barry upon seeing him back, and Cindy Simone, who was a mutual friend of Sara's, Thea's and Roy's, and Ray Palmer; and they all celebrated Barry's return with Caitlin and Cisco. Even Diggle decided he'd join in on the fun, given that Oliver and Thea were friends with Barry.

Even though Barry and Caitlin couldn't get drunk, they decided to join in on the drinking anyway as they raised their drinks along with the rest of their friends. "To Barry and Team Flash." Oliver said, which they all repeated the toast before downing their drinks and enjoyed their evening together as they drank, listened to music, dancing to the music...okay, some of them did, Oliver and Diggle definitely didn't..., and overall having a genuinely good time....but none of them knew just what lay ahead...and for one of them in Team Flash, things would soon change.....

Author's Note: I hope you enjoyed this chapter for the story. It took a lot longer than I would care to admit to think of this chapter, as I've been a lot more busy than I'd care to admit, but it's done now. There are some elements to it that might be a little familiar, if only subtly so, and I thought it wouldn't hurt to bring in Team Arrow to the mix as well. Also, yes, this chapter is completely of my own devising and not related to any episode of The Flash, so I'm hoping you like it.

What did you think though of Team Arrow's and Team Flash's little "chat" with Killer Frost? Was it too much, or was it okay? I'm a little mixed on the results, but I'm hoping you guys liked this chapter. I can't promise when the next chapter will be, or what surprises can be expected from it, but I'm hoping you'll be pleasantly surprised with or shocked in a good way. Anyway, I hope you all enjoyed the chapter, and I hope you all have an amazing day!