In which Leonard "wakes up" the day before (specifically, the day the Santinis managed to get the jump on him and Mick, if you'll recall the way they entered the episode Rogue Time) and tries unsuccessfully to process what just happened?
And then we go back to the Waverider as he finishes his narrative and Rip explains why things happened the way they did, and why changing his history is a Very Bad Idea.

"That bastard" (well, one of them, anyway, mentioned in passing) copyright to me. One of these days I'll come up with a name for him, but the characters referring to him that way certainly fits.
All other characters mentioned or seen this chapter copyright to DC, CW, etc.

Leonard huddled on the road, his chest burning where the rebar pierced him, heard a squeal as the storm continued to tear the city apart, as he waited for Thawne to pull the...

Wait.

Road?

He cracked one eye open... then the other.

Everything was still dark.

He opened his eyes wider. No, not everything. A light off to the side proved to be his motorcycle, lying where it had fallen after it slid out from under him. He could just make out the front tire spinning.

He blinked several times until he could see properly. His vision was still dim, but it was broad daylight, not at all like that morning's storm had been. No, this looked like... the day before?

The lights further out were from the truck. The squeal he'd heard must have been Mick, slamming on the brakes right after he'd seen Leonard go down.

"Len? Lenny!" Two pairs of footsteps ran for him as he attempted to push himself up off the road. "Lenny, are you okay? What happened?" Lisa crouched down beside him and tried to help him stand.

He yelped when she touched a sore spot on his chest, startling her into letting go of him. He fell back to his hands and knees, shaking violently.

Mick crouched on Leonard's other side, but didn't try to touch him. "You're not getting sick again, are you?"

Leonard shook his head. He didn't think he was sick. He quickly took stock of his condition. A few scrapes, where his riding gear hadn't quite been up to the task of protecting him from the fall. That sore spot on his chest, and another on his back; he must've hit the steering column on the way down.

The cold pressure against his temple was the metal buckle on his helmet; it had somehow pushed up past his ear when he'd fallen.

Nothing broken. No serious damage.

But he couldn't stop shaking.

"Lenny, say something!" Panic crept into Lisa's voice, a note of fear she hadn't used since the last time their father had attacked them. "Look at me, please!"

Leonard tried to obey, to reassure her that he was all right, but for just one moment, all he could see was the mess he'd found under the debris...

As before, he barely managed to turn away before he lost control of his stomach.

This time, however, there was something in his stomach to reject.

Mick didn't quite move fast enough to avoid the splatter zone. "Disgusting," he muttered.

"You are sick," Lisa said. "Maybe we should stop going to the Motorcar. If their food isn't agreeing with you anymore—"

"N—no," Leonard replied through chattering teeth. "It—isn't them. It's Mar—Mardon."

Mick and Lisa shared a worried look. "Who... who's Mardon?" Lisa asked.

"Met—meta—human," Leonard tried to explain. "Controls—the weather." He finally managed to get to his feet, but the effort made him dizzy, and he was so weak he had to lean against Mick to keep from falling over again. "We—we need the guns—from Star Labs."

"What, did you forget?" Mick scoffed. "Cops had those things destroyed."

"Ci—Cisco Ramon," Leonard said. "He—built them. He can—build more."

"Maybe you should lie down for a while," Lisa suggested. "We can talk about this when you're feeling better."

"No!" Leonard snapped. "We need—those guns. Can't let him—destroy—the city."

Mick looked around warily. "You guys," he said, "I think we're being too loud out here."

Lisa nodded. "All right, Lenny. If it'll keep you quiet, I'll go see what I can do about this Cisco." She looked up at Mick, not even bothering to hide the tears in her eyes. "Take care of him. Please? This can't be like last time. It can't."

"I'll do what I can," Mick promised.

Lisa helped Leonard remove his helmet so she could strap it on her own head before she pushed his bike upright, mounted, and sped off back towards the city.

"Come on, Len," Mick said. "Lisa can take care of Cisco for you. Let's get you warmed up, okay?"

Leonard wanted to protest, but most of his strength was spent from shaking so much. He barely made it a few steps in the direction of the truck before Mick just picked him up and carried him over.

"You're too light," Mick grumbled as he set Leonard in the passenger seat. "You know that? Even with all that heavy gear on. Too scrawny."

Leonard tried to snicker at the complaint. All that came out was a quick puff of air.

"I got some blankets in the back," Mick said. "You going to be okay while I grab them?"

Leonard nodded. "I think so," he murmured.

"At least you've stopped shaking," Mick said as he walked away.

Leonard closed his eyes while he waited. He was fine. He wasn't getting sick, not like... not like the other times. The hours he'd put into planning this heist were wearing him out. That was all. He just needed to rest...

A stone clattered somewhere ahead of him. Someone bit back a curse.

Leonard opened his eyes. "Mick?" he said, his voice barely more than a croak. He twisted around to peer through the open back window, but the arsonist was still rummaging around and hadn't heard him.

Leonard's eyes closed again...

Then snapped open wide. That sound had come from ahead of them.

He was really worn out to have missed something that obvious.

"Mick?" he called again a little louder. He reached for his gun...

And his hand met empty air. Damn it, of course Mick had taken his gun; neither he nor Lisa liked letting him have a weapon on him when they thought he was sick.

The passenger side door yanked open, and Leonard found himself staring straight into the barrel of a revolver.

"Mick!" Leonard called once more. He tried to back away, to scramble to the other side of the truck, to keep the owner of that gun from touching him. He almost fell out when the driver's side door opened up behind him.

"Oh, shit, Len! Hold on!"

Leonard fought tooth and nail to stay free of Santinis' thugs until Mick could reach him, but two more sets of hands dragged him out and pinned him to the ground. And even the rush of adrenaline wasn't enough to overcome his weariness...

The last thing he saw was the bag descending. Then a sharp pain in the back of his head, and everything went white... then pitch black.

—

"And the rest," Leonard said, "as they say..."

"Is history," Mick finished.

Rip groaned. "So much for private," he muttered. He glared at Jefferson.

"Don't blame the kid," Mick said. "I made him talk." He stared at Leonard. "That can't have been real. What you saw... you were sick. Delirious. That couldn't have happened."

"Felt real," Leonard murmured. He continued shivering on the floor.

"It was real," Rip replied. "There are a few details Mr. Snart was vague on, things I assume he is afraid to remember, but the incident happened exactly as he described it."

"That why you don't want me killing that bastard?" Sara muttered to Rip. "I mean, I know you said Leonard would still remember, but I never imagined it could be that bad."

"That's a very small part of it," Rip muttered back, "but yes."

"Then... how are they still alive?" Kendra asked. "If all of that actually happened... Wait... the Flash?"

Martin nodded. "That must've been from the first time he went back in time," he said.

Leonard looked up at the professor. "I'm sorry, I must not have heard correctly. You said the Flash went back in time?"

"Er... I... I wasn't with the team at the time," Martin admitted, "so I don't really know all the details, but, uh..."

"Ah, perhaps Gideon could be of service?" Rip suggested.

"Yes, Captain," Gideon replied. "When Mark Mardon, the metahuman known as the Weather Wizard, threatened to destroy Central City with a tidal wave, the Flash used his speed to generate a wall of wind to drain the wave of its power. In the process, several factors combined to cause him to go back in time a short period... a little over two nights. Despite frequent warnings from Eobard Thawne—known to the Flash at that time as his mentor Harrison Wells—to not interfere with the timeline, the Flash set out to prevent Mardon's attack before any of his friends could be harmed. It would seem that Mr. Snart's disorientation, when he lost control of his motorbike, coincides with the moment the Flash altered the timeline by capturing Mardon."

"Coincides with... or was caused by," Rip said. "I'd wager the two timelines snapping together might've affected you just a bit."

"You mean we have the Flash to thank for the fact that we're alive?" Mick said. "Well, shit." He shook his head. "If I'd had any idea... I never would've let you go after that emerald. Sure as hell wouldn't have let you give it to your old man."

Rip stared at the arsonist in astonishment.

Leonard, however, quickly got over his surprise and looked pissed. "You would've stopped me," he snarled. "Knowing what that bastard's done to Lisa, to me. You would've stopped me from trying to change it?"

Mick nodded. "Yeah. I would have. You have no idea how dangerous it was to try what you did."

"So people keep telling me," Leonard muttered.

"But why?" Sara asked. "Speaking as someone who's actually been dead in this timeline, I'm sure remembering something like that is disturbing as hell." Leonard and Kendra both nodded. "But how could changing it be any worse than leaving the original timeline intact?"

"I'm agreeing with Sara," Kendra said. "Now that we know, now that Snart knows... It's at least something we know to watch out for. Right?"

"Mr. Snart's case is a trifle more complicated than that," Rip said.

"Because of his eidetic memory," Jefferson replied. "That's what you told Grey, right? But you also said you can monitor Snart's timeline so long as he's on the Waverider, keep the damage to a minimum. Why is that so complicated?"

"Why did he get sick?" Mick asked.

"Thank you, Mr. Rory," Rip said. "That's why it's complicated. Mr. Snart, when you've experienced the flash sideways, you also became considerably ill, am I correct?"

"Who wouldn't, after seeing something like that?" Ray asked.

"Not that kind of illness, Dr. Palmer. No, this was a temporal illness. Not unlike the side effects from time travel, but in this case..." Rip sighed and looked down at the trembling thief. "In your case, Mr. Snart, that illness came from your difficulty reconciling the two distinct timelines. The more drastic the change, the more severe the illness."

"Speaking as someone who's reincarnated a few hundred times, you really can't get more drastic than dying," Kendra said.

"Er, technically you can," Rip said. "The type of change is certainly relevant; that's why his father going to prison for a slightly different crime didn't have any effect, and why his biggest problem with Tess was taking nearly three years to reject that timeline."

"Biggest problem?" Mick echoed.

"Insofar as the temporal illness is concerned," Rip amended. "Diagnosing and treating the illness is a completely different problem. But as I was saying, the most significant factor is time; how much of his life had changed."

"And when the Flash stopped the Weather Wizard," Martin said, "that only changed a couple of days. Right?"

"Correct. But changing the last forty years of his life?" Rip shook his head. "If you had been successful, Mr. Snart, the disparity between the timelines would almost certainly have killed you. I trust you can understand why I must caution you against trying to change your own history?"

"Because it's dangerous," Leonard replied. "To me."

Rip nodded.

Leonard smirked. "But there's one thing you keep forgetting, Rip. The only thing I care about is protecting Lisa. Now can you tell me, if I'd succeeded, if I had made my father... better... Can you honestly tell me Lisa would not have been safer?"

"You stubborn son of a bitch," Rip grumbled. "You would throw your life away for a chance to make things even a tiny bit better for your sister?" He couldn't decide whether he should be angry at the man or respect him for his dedication.

"You wouldn't do the same for Jonas or Miranda?" Leonard countered.

"That question is not fair," Rip said. He sighed. "I... I'd prefer to stay alive to protect them, but if I honestly believed it would make a difference... yes. I would sacrifice myself for them."

"Well, then, Time Master," Leonard said, "as I asked... can you tell me she wouldn't be safer?"

Rip shook his head.

"I can," Mick said.

Leonard quirked an eyebrow at his partner.

"Funny thing is," Mick explained, "all this trouble is because of your so-called perfect memory, but you don't even remember what you did. All the times you've complained about us taking away your weapons, about Lisa bringing in help when she checked up on you..." He shook his head. "I remember the earful you gave me after she made Cisco help her that one time. And as smart as you are, you've never even asked why."

"Maybe I didn't think I'd like the answer," Leonard admitted.

"Damn straight you wouldn't," Mick replied. "First time you got sick like that... first time we knew about, anyway... you didn't even recognize us. And I don't know if you thought you were being attacked, or what else was going on in your head, but... You pulled a gun on her, Len."

Leonard's mouth dropped open.

"You tried to shoot your own sister. Nearly shot me, before you realized who we were. Scared the hell out of us."

"That's why I don't want you to kill that bastard," Rip muttered to Sara.

Next chapter... aftermath. No more back and forth between Legends and The Flash (I think), just different scenes that didn't necessarily appear in Rogue Time, but occur around the same time, as Leonard tries to cope with this experience.
And you have officially caught up with me; while I have written several chapters ahead in some of my fics, this is (at the time of posting) the last thing I've written in this one. Hope to get started on the aftermath soon! To be updated after I've re-watched Rogue Time... when my work schedule allows.

And I have officially begun confusing myself with this whole deal of changing how I refer to Len based on who the viewpoint character is. So I'm going to start editing my older chapters and just call him Leonard in the narrative. This will make all characters go by their given/first names regardless of how the other characters would typically think of them.
Unfortunately it won't be a simple "find/replace-all"; dialogue will still depend on who's speaking, of course...

Minor edit:
Originally Rip just said about the memory of Tess was that the biggest problem Len faced was how long it took to reject the timeline. In that version, Mick did not react to the notion that that was the "biggest" problem, because it really was the biggest problem.
Well... I'm serious, my muse clearly hates me, because it can't stop coming up with ways to hurt my favorite characters. Though to be fair I did already include hints before my muse had actually dropped this particular bomb on me.
Let's just say I"m trying to decide if the name of Tess should be another trigger for Len, though making it so would require more significant modification to a scene in chapter one. You'll see why it could be a trigger when I get around to writing What Could Have Been (which is about Len's memories of the timeline the Reverse Flash prevented) and also in League of Macguffins (which is about the team's quest to fix whatever the League did to Len in Majummed).

'Nother minor edit.
In Out of Time, the dinner Cisco refuses to go to seems to be the same night Mardon attacked that coroner (why else would Wells be asking him if he's supposed to be getting ready?)
In Rogue Time, the dinner appears to be the next night.
I'm editing for the Rogue Time version of events, seems to work a tiny bit better for me.