Disclaimer: I do not own Smallville or The Flash.

A/N: This fic is a prequel to both "Heroes Unite, Aliens Invade" and "Two Earths Join Forces Against Another". It details what happened during Barry Allen's initial trip to the Smallville Universe, which is known as Earth-21. Takes place during The Flash Season 2 and roughly five years after the Smallville series finale. The Smallville Season 11 comics are completely ignored.

Chapter 1

"Okay, you guys, I'm here," Barry Allen announced into his comms. "You got my location?" He was standing in an open grassy area in Keystone City, while the rest of Team Flash was inside the cortex of S.T.A.R. Labs back in Central City.

"You good? You don't need to, like, stretch or something?" Barry heard the voice of Cisco Ramon ask.

"No, no, no, I'm good, I'm good," Barry answered.

"Let's take this Tachyon enhancer out for test drive," Cisco said.

"All right," Barry said, the silver Tachyon device clutched in his hands. He attached it to the emblem of his Flash suit. Almost immediately, the device glowed bright blue, sending a sudden surge of energy flowing throughout his body. "Ooh, yeah, I feel that."

"That is the Tachyon device powering up the Speed Force in your cells like a quick-charge battery," Caitlin Snow explained. "How do you feel?"

"Different," Barry answered.

"Let's see how long it takes for you to get back here," Cisco said. "On my count. Three, two, one, go!"

With that, Barry whooshed off faster than a bat out of hell, the powerful gust of wind left behind in his trail causing the 'Welcome to Keystone City' sign to fall down. Indeed, he was moving significantly faster than his usual speed limit, which meant the Tachyon device was working exactly as it should so far. He would finally gain what he needed to defeat Zoom, the villainous speedster from Earth-2 who had spent the past several months antagonizing Barry and his friends. To add insult to injury, about two weeks ago, they finally discovered Zoom's identity and, much to their immense shock and horror, found that the man beneath the demonic mask was none other than Jay Garrick, who, not dissimilar to Dr. Wells/Eobard Thawne a year earlier, had convincingly presented himself as a 'helpful ally' to Team Flash while secretly being the very threat they were trying to put an end to. Then, a few days ago, having grown more determined than ever to stop Jay/Zoom for good, Barry had traveled one year into the past to seek Thawne's assistance to increase his speed. While the time travel trip hadn't gone according to plan, what with Thawne figuring out that Barry was from the future and the latter being pursued by a Time Wraith sent by the Speed Force itself, Barry managed to get exactly what he needed, which led him to currently testing out his speed with the Tachyon device.

"Guys," Barry announced, "I can go faster!"

"Do it," Cisco responded.

Barry immediately increased his speed even more. Suddenly, a portal appeared before him and he ran directly into it.

Completely unaware of what had just happened, Barry reemerged from the opposite end of the portal and continued moving across the country at speeds incredible even for him. He finally slowed down when he noticed an apartment building severely on fire. He super-sped into the burning building and started doing his work to extinguish the flames.

Clark Kent and Bart Allen were, for what had to be about the hundredth time since they'd met all those years ago, racing each other throughout the country. As always, Bart was ahead of Clark. The former was running on solid ground, while the latter was flying. They were clad in their Flash and Superman costumes, respectively.

"Always too slow, Supes!" Bart quipped.

"I'm just taking it easy on you, Bart!" Clark countered.

"Oh, yeah?" Bart said, skeptically. "So, does that mean you take it easy every time we race then? Because I cannot think of a time when you actually managed to beat me."

As the two of them arrived back into the city limits of the beloved Metropolis, they noticed a burning apartment building and immediately rushed inside. Upon entering, Clark and Bart spotted a guy, clad in a dark red full-body suit that covered everything but his eyes, nose, and mouth, had beaten them to the scene and was rapidly spinning his arms around in an effort to kill the flames.

"You look like you can use a couple of extra hands with that," Clark offered, as he and Bart appeared next to Barry.

"No, I'm good, I got..." Barry began, but suddenly became speechless as he noticed the smaller guy, clad in a dark red suit with a domino mask, also started spinning his arms around, while the bigger guy in red and blue simply started blowing out the flames with his super-breath.

Once the fire was completely out, Barry turned to the two heroes, a look of surprise on his face. "You're... who are you guys?"

"I'm Superman," Clark answered, as if it was supposed to be the most obvious thing in the world.

"You're who now?" Barry asked, frowning.

"Superman," Clark repeated, also frowning. "Surely, you must've heard of me."

"No, I don't think so," Barry said, shaking his head.

"Dude, are you just joking or have you been living under a rock your whole life or something?" Bart remarked. "Everybody knows who Superman is! Just like everybody knows me, the fastest man alive!"

"What?" Barry muttered at Bart's 'fastest man alive' comment.

"Now, the question is who are you?" Clark said to Barry.

"I'm The Flash," Barry answered, his frown deepening. How could anyone not know who he was after almost two years?

Bart abruptly burst into laughter. "Sure you are."

"What?" Barry said. "No, really, I'm The Flash, the fastest man alive."

"No, I'm the fastest man alive!" Bart protested, defensively. "And I hate to break this to you, stud, but The Flash is my codename and it's already been trademarked. So you gotta come up with your own. You can have Impulse if you like, though. I pretty much kicked that name to the curb a few years back."

Barry was puzzled. Where had another Flash come from? The only other speedster he knew of who was also known as 'The Flash' was Earth-2's Jay Garrick, or so he'd thought. The thought of Jay caused Barry's anger towards the man to suddenly flare up again. He still couldn't believe it. The same guy who'd taught him how to throw a bolt of lightning was also the one who'd brutally broken his back, publicly humiliated him in front of most of Central City, and left him crippled for days. Was Barry really so blind and gullible that he couldn't see right through Jay's deception? Had he not learned his lesson at all after everything that Thawne/Wells had put him and the other Team Flash members through the year before? Apparently not. If there was one person on the entire planet who deserved a medal for falling into the same trap twice in a row, it was Bartholomew Henry Allen.

Focusing his mind back on the current situation, Barry looked at Bart and said, "No, The Flash, that's me, uh, I'm The... wait, do you guys not know who I am?"

"Can't say that I do," Bart answered.

"Same here," Clark added. "I mean, even if you're implying that we should know who you are, I'm pretty sure I would've recognized you from the newspapers or TV if I'd seen you before, but I don't. I'm sorry."

"And you're known as The Flash too?" Barry asked Bart.

"Yep," Bart answered. "Fastest man alive!"

"But I thought I was..." Barry began, and suddenly paused. "I didn't know there was another speedster out there with the same name as me. I mean, I've been The Flash in Central City for almost two years now, ever since I was struck by lightning the same night the particle accelerator exploded and got my powers."

"Two years?" Bart repeated. "Dude, I've been living in Central City for a while now and I assure you, I've never heard a thing about a second Flash running around and doing the whole superhero thing just like me."

"Second Flash," Barry muttered, taking in Bart's words. "How long have you been in Central City?"

"It's going on about, um, seven years now," Bart answered.

"Seven years? So you got your speed the same way I did from the particle accelerator two years ago?" Barry deduced.

"To be honest, I don't have the slightest clue about this particle accelerator thing you're talking about," Bart said. "Besides, I've had my speed a lot longer than just two years."

"Okay, but if you're from Central City and you're a speedster like me, how come you don't know anything about the particle accelerator or its explosion?" Barry asked. "What about S.T.A.R. Labs?"

"Yeah, I know a place called S.T.A.R. Labs, but it's not even in Central City," Bart answered. "It's actually right here in Metropolis."

"Metropolis?" Barry questioned, having never heard of a city by that name before. "Where's that located?"

"You're in Metropolis right now," Clark clarified. "Metropolis, Kansas, to be exact. It's your first time here I assume?"

"Yeah, it must be," Barry muttered. He pondered for several moments, trying to figure out what was going on. He'd never heard a thing about the red and blue caped hero named 'Superman' or a second scarlet speedster running around Central City and protecting people. And what had the latter meant by S.T.A.R. Labs not being in Central City, but located in some city called Metropolis? "Oh, boy," Barry sighed, as a realization suddenly hit him like a flash of lightning, pun intended. He only hoped he would be wrong, though. "Hey, do you guys mind waiting here for me?" Barry asked Clark and Bart.

"Waiting here for what?" Clark asked.

"I think I'm starting to figure out what's going on," Barry explained, "but I need to know for sure if it's the case. If it is, I think I'm gonna need you guys' help."

"Okay, we'll wait for you," Clark nodded.

"Don't expect us to be waiting around here all day, though," Bart added.

"No, I'll be right back here in, well, a flash," Barry promised, and immediately whooshed off.

"I wonder how that guy will do if I raced him," Bart said. "He'd probably do better than you, no offense. So, are we really gonna just stand here and wait for a guy we don't even know? I mean, what if he doesn't return?"

"Well, he did say he might need our help with something," Clark pointed out. "Not that we know what that 'something' is, but I think we should give him a chance."

"And how can we be sure we can even trust him?" Bart countered.

"We'll give him the benefit of the doubt for now," Clark said. "If does something that proves otherwise, that's when we'll cross that bridge."

Suddenly, Barry whooshed back into the burnt apartment building. While he was gone, he'd checked out Central City and noticed that, while it was located in the exact same spot and had, more or less, the same layout, his city looked quite different than the way he remembered it, complete with the total absence of the highly recognizable S.T.A.R. Labs building. That confirmed exactly what he'd started thinking. Due to having run so fast with the Tachyon device, he had inadvertently traveled to another Earth.

"Okay, guys, I'm back," Barry announced.

"Where did you even go?" Bart wondered.

"Central City," Barry answered, "and confirmed exactly what I was thinking." He pulled down his cowl, revealing his face to the two other heroes. "My name is Barry Allen, and I am the fastest man alive. I also think that I am on the wrong Earth. I'm gonna need your help."

Clark and Bart exchanged stunned glances, as both of them allowed their minds to process what Barry had just told them.