A/N: Thank you all very much for the support and love! School's kicking in like usual, but I'm planning on continuing this and some other stuff regularly. Thank you very much to BateShot39 and Fleetlord Avatar for following and favoriting this, and the reviews were spectacular. Speaking of which...

Shian1998: Thank you! Sonic and Barry's friendship is definitely going to be explored here. As for Eggman, he'll reappear soon...

Fleetlord Avatar: Thank you very much! I'm glad you're enjoying this, especially as your Zootopia/Flash crossover was excellent writing. That robot theory will be addressed soon. As for a race? Consider that a running gag for now (no pun intended!)

So without further ado, chapter four!

Chapter Four

Running to Get Home

Two colorful presences, one blue and one crimson, darted to the front porch of a secluded laboratory located on the edge of the city. Sonic was first, his quills flexing as he steadied himself, and right next to him stopped his new ally, the Flash. He panted while looking up at the house they were gazing at.

"Your friend…he lives here?" Barry asked curiously.

Sonic shrugged. "Yep. Tails likes the peace and quiet, but then again, he isn't a smart fox for nothing. The concentration helps with his work."

"Trust me, I understand," the scarlet speedster commented as they walked up the steps. "My best friend's a tech genius who also moonlights as a pop culture dictionary."

"Really?" Sonic looked amused. "Do you get most of his references?"

Barry laughed. "Most of the time. But it's nice to have somebody you can just chill with." The hedgehog nodded and opened the door, Barry following him inside. He saw that the lab was a good-sized space filled with a worktable island, racks of equipment, computer monitors, and a refrigerator. As he neared the latter, he saw that a photo of Sonic and a yellow fox was plastered onto the surface by magnets. The image made him smile at how happy they were.

His attention was pulled away by a loud CLUNK! In the distance. He looked back, as did Sonic, when the same yellow fox from the photograph emerged. He was scrawny but soft-furred, with blue eyes and the exact same gloves Sonic was wearing. Then he noticed the two tails emanating from behind him, making him all the more curious.

"Oh, hello…" Tails stuttered at the two of them. "Sonic, I wasn't expecting you back so soon…with a friend?" His expression locked onto Barry, puzzled by the masked man and the specific design of his outfit.

"Tails, meet the Flash," Sonic pointed out. "He's the lucky guy who found – actually, had – the Chaos Emerald we were looking for." To prove his point, Sonic produced the jewel out of his hand and twirled it around a bit.

"Wha-wow!" The fox rushed over to his friend, accidentally knocking a couple of loose tools over in the process. "That's amazing…but how'd-sorry, I mean…you're called the Flash?" He asked, looking over the new arrival, who held his hand out in a friendly gesture.

"The one and only," he replied politely. "Nice to meet you." Tails took his hand and shook it heavily.

"But why's that your name?"

Before answering, he looked to the discarded items. "Just watch." In a splash of incredible light and energy, he shot around the room. Tails could only gaze and be transfixed by his lightning, whereas Sonic leaned against a table. When he stopped in front of the fox again, the room was much neater than it had been a few seconds earlier. "That's why."

Tails' eyes enlarged. "You're fast…" he breathed. "Maybe…just as fast as Sonic?"

The two speedsters exchanged looks, then laughed dryly at the idea.

"Eh…I wouldn't push it right now…" Barry pointed out. "Though I'm not against a friendly race."

"Me neither," Sonic lamented, "but we've got way bigger fish to fry. Like the Chaos Emerald, for instance."

Tails looked to the emerald and then to the superhero in their midst. "All right…I think I get that you're a speedster. And from the looks of it, probably not from around here. But how did you get your hands on Sonic's emerald?"

"Honestly? It's a lot to explain…" he trailed off and then shrugged, "…but considering my circumstances, I might as well tell you." He moved back and sat on the nearest worktable, then cupped his hands together and looked down. "What have you guys heard about alternate universes?"

"Outside our multiverse?" Iris asked disbelievingly. "Is that even possible?"

Harry massaged the bridge of his nose; elaborating on science today was really starting to tire him out. "I'm not saying it's the exact truth, but my readings didn't detect a breach. And, if my word is somehow not enough, Ramon…" he gestured to the junior scientist, perking up at his mention.

"Right back to what he said, Iris," Cisco added. "I couldn't get a lock on where Barry is from those particles. Earth-15, Earth-2, even Earth-X…nada."

Ralph's brow fluttered and then lifted, an idea in his mind. "Wait a minute…Allen's powers come from that Speed Force stuff, right? Why not build a doohickey or something and track him with that?"

Caitlyn sighed. "We'd need more than particles to track him, Ralph. Then you'd have to take into account all the different speedsters in the multiverse, and the- "

"We get it, we get it!" Joe exclaimed frenetically. He stared down at the monitor, sighing with his fists planted even on it. "Seems like whatever we try is going to end up a loose end."

Nervously, the rest of the group didn't speak, the silence almost sickening. But then, Iris breathed in and whirled around, determination coursing through herself.

"Dad, no. We can't give up." Her chest heaved as she continued. "Barry's been lost before…stuck in the Speed Force, alternate dimensions…Heck, he fought an emo version of himself that came from the future. And we've found him again and again. We. Did. Because he's our family and the heart of this team. So there has to be a way. I know there is."

Caitlyn shifted in her spot, gripping her arm with the other hand. "Iris, don't think for a second that none of us want to find him," she mentioned. "He's helped us all in our own ways…but this kind of math and science is beyond what we normally deal with."

"Actually…" Everyone looked to Cisco, nervously on the brink of spilling something. "There might be someone who has better experiences with dimensional travel…that could help us."

Harry didn't act fazed at the mention. "Are you talking about whom I think you're talking about?"

Cisco smiled. "Trust me, she's the best at this. I mean, other than me."

Tails poured a cup of coffee for himself and drank it, but even something that sugary had no effect on his mind. Not after the mind-blowing revelations he'd heard from the Flash.

He'd gone on for minutes and then an hour, rambling about many things the two of them never considered before. Apparently, multiple universes with small or massive differences existed, separated by the unique frequencies they vibrated at. From what the human speedster had told them, making powerful enough energy was the best way to cross over dimensions. And thanks to his running, he'd done this time and again – though he mentioned that a good portion of the worlds he went to weren't the best.

Then he went into his origin. His own mother being murdered, his father thrown into jail, and then the lightning years later…Tails' might've said it was a sped-up tale, but that'd be getting too literal. As Barry (yes, that was his name, spilling it after pulling his mask down to reveal a human face) mentioned, he'd fought metahumans with the power of science fiction and other super-athletes with the mindsets of gods.

He and Sonic were humbled. Their exploits had saved the Earth time and again, even taking on mystical and alien foes far greater than Eggman. But the yarn he was spinning seemed to be on another level entirely.

When he'd finished, the blue hedgehog blinked his eyes twice and breathed in. "Crazy…so you fight crime as a superhero?"

"Yeah," Barry confirmed, "though that's not my whole life. I'm a forensic scientist for my city's police department, so I'm examining crime scenes when I'm not running around."

Tails perked up at the revelation. "Gee. It seems handy being a scientist and a superhero in one, right?"

"Sure…" Barry scratched the back of his neck and looked down. "It's a lot more dangerous than it looks, though. Having this kind of power…it makes you see weird stuff sometimes."

"Try me," Sonic challenged lightheartedly. "I've been a werewolf and taken down a corrupt king Arthur."

The human snorted. "Uh, well besides fighting speedsters with god complexes for three years in a row, I've never gotten my hands on a nuclear emerald before, let alone one that sent me to a parallel universe." He looked back to it, lying neatly on a far-off counter. "Just what exactly is that, anyway?"

"Glad you asked," Sonic quipped as he scooted off and nabbed the emerald in his palm. "It's called a Chaos Emerald. There's seven of them, and each one contains stuff called Chaos Energy. With one, you could power a machine or get stronger. Collect all seven? You'd be near-invulnerable."

"What, they can just give you ultimate power? Barry answered.

"In a way," explained Tails. "Finding them is the tricky part because everyone seems to always be fighting over them. Half the time, they're getting lost across the planet.

"That's why Eggman's always trying to nab them from us," Sonic added. "He either wants them to build new machines or take over the world." He smiled mischievously. "Maybe they're the reason his ego's so inflated."

Barry's brows sunk into confusion. "Another thing. Who's this Eggman guy you're talking about? He sounds like an egomaniac."

Sonic chuckled, leaning against a table parallel to Barry's position. "That's because he is. He's this brilliant inventor with a crazy IQ, but he considers himself better than everyone else. So he builds massive, destructive robots to constantly wreak havoc.

"You could say he and Sonic have a rampant rivalry," said Tails. "He's always plotting to take over the world, but Sonic stops him every time."

Barry prepared to react, then paused and thought on his words. "You know, that sounds a lot like the guy I'm facing right now back on my world. He's called the Thinker. He's this metahuman with an amazing intellect, but it's killing him, so he's finding and taking over the bodies of other metas."

"That sounds sick," Tails replied.

"It is," Barry continued, "but what's worse is that I don't know what his endgame is. For the moment, he's been quiet. And I can't help wondering if he's started hurting people again…Just when I'm off somewhere else…"

Sonic saw the worry in his face and straightened up seriously. "Then let's help you get back, okay? It's the least me and Tails could do. Right, bud?"

The fox collected himself into a positive stance, walking to stand next to his friend. "Yeah! I'll do my best."

Barry's gaze lightened up again as he stood up. "Thanks. Where do we start?"

"Right…" Tails put a finger to his chin. "Maybe if we want to figure out what's wrong with the Emerald, we should do some physical testing."

"Like a short jog?" Sonic poised.

"Not necessarily," concluded tails. "I think it'd be better if we recreated the position you were in that brought you here."

Sonic looked to Barry. "I guess it's time for a tag-team jog."

The park was located at the tip of Central City, flowers blooming and birds flying around. Yet the fire and subsequent explosion earlier seemed to cast a dour mood over it, and nobody could be seen walking in it. Then a breach opened up and spat Cisco out onto the pavement. He collected himself and looked down the park path, seeing nobody in the vicinity.

"You sure picked the right spot, Cisco," a warm voice floated down the back of his neck. A swirl later and the familiar eyes he adored were there. "No people, calm atmosphere. Just the right place for a meetup." Her warm smile was temporarily hidden behind a flowing curl of black locks.

He put on a smile. "Good to see you, Cynthia. Really, I'm so happy we get to see each other outside of your job."

"Me too, amante," she vocalized softly. "Where else in the Multiverse am I supposed to get coffee?"

He chuckled slowly.

"But that's not why you called…is it?" Her eyes shone a quick glare at him, signifying that the gig was up.

"Points to figuring it out." The happiness shrank from his face as he paused. "My friend, Barry? He's gone."

Grief washed over her, building to a slow response. "Oh, Cisco, I'm so- "

"No, no!" He exclaimed. "Not that kind of gone. He's not dead, we know that, just lost somewhere. But we don't know where."

The look of grief on her face was instantly replaced by skepticism. "This has happened before, right? Just check the other earths."

"That's the thing…" Cisco trailed off steadily. "He had this emerald with some crazy energy in it when he disappeared, and the particles that he left at the site of his disappearance don't match up. I mean, they don't lead me to any one of the fifty-three earths."

Her eyes froze. "Cisco…what color did this emerald shine when it went off?"

"Green. Why?"

"You're not dealing with a gem. You're dealing with a Chaos Emerald."

The Flash and Sonic stopped just short of the city's edge, arriving at a large patch of barren wilderness. Mostly manila sands, there were few pieces of nature you could see inside. Sonic gazed up and down the spot before looking back to his new acquaintance.

"All right, this is the place. You ready?" He asked.

The scarlet speedster nodded, noticeably concerned about something. "Think so. It's just kind of déjà vu – dealing with this all. It looks a lot where I was when I – you know – disappeared."

Sonic grimaced slightly, giving him an arm pat. "Don't worry. I'll be keeping up with you and making sure this all works out. You're gonna' be fine."

Barry nodded heavily. "Okay. Here goes nothing…" He held his hands out and pulled them back. When the lightning coursed into his vision, he was off and left a blast mark in his starting spot. Sonic bolted right after him to keep up.

Scurrying at a rapid pace through the vast environment, he felt his speed picking up. The wind chocked and tore at his costume, and the recent events were clouding his mind. But, remembering Iris, everything cleared, and he kept going forwards. He looked back at Sonic briefly, slowly catching up but still a short distance behind his acceleration.

His feet started getting heavier. As he tried to keep his eyes open, a lightness spread over his body. He saw a vivid blink far ahead. It was a breach! It had to be. Everything else, Sonic included, seemed to filter into the back. He was getting closer and closer, his speed making the lightning heavier than normal. A gloved hand reached out…

Something had gone wrong. His feet were no longer on the ground. The world tumbled sideways and he felt himself flying off the ground. Suddenly, his eyes zeroed in the approaching sand and he let out a yell. After that, nothing was visible.

From far away, a worrisome cry sounded.

Another crazy ending. These may seem a big drastic, but they're supposed to make the stakes feel more real and dynamic. Anyways, all I can tease for next time is some progress on both ends, as well as for our up and coming baddie. You could say he's got some Metal in his sleeve...Adios, folks!