In which my efforts to fix some minor details totally screw me up and I accidentally replaced chapter 1 with chapter 4. And I didn't notice until I came in here to fix some other minor detail.
Oops. Fixing the chapter is easy enough... fixing the notes, not so much. And fixing things for any readers who might've come across this while the wrong chapter was in place... yikes.

Anyway, a story in which Leonard Snart's eidetic memory has serious consequences when attempting to change history.

Here we have a simple framing story, taking place on the Waverider, with Rip discussing the theory of eidetic memory vis a vis time travel and trying to make sure Len understands why changing his own history is a Bad Idea.

All characters mentioned or seen this chapter copyright to DC, CW, etc.

"A word, Mr. Snart?" Rip said. "In private, if you please."

"Ooh, looks like someone's going to the principal's office," Sara said with a laugh.

Leonard refused to dignify the remark with even a glance her way. But when Mick got up to follow, he paused for just a moment. "Private means no eavesdropping, Mick," he said over his shoulder. "I think I can handle myself against our... honorable captain."

"Yeah, whatever," Mick grumbled. "I was just getting a snack."

"Hmmm... of course you were," Leonard replied before he followed Rip into the captain's office. Once inside, the door closed and locked itself behind him, and Leonard folded his arms and sat on the desk, waiting for Rip to speak.

At least five minutes of silence passed before Rip sighed. "To be fair, I am the one who asked to speak with you," he said, "not the other way around."

"About what?" Leonard said. His usual smirk was more pronounced at his obvious enjoyment of the captain's discomfort.

"What were you trying to do?" Rip said. "With that emerald, I mean."

Leonard shrugged. "I already said I won't apologize for that," he said. "This mission has always been about saving your family; I'm just as determined to protect mine. I know," he added, holding up one hand, "I know. You're the time master, I'm just the thief that time forgot. So you can spare me your lectures about changing history."

"No lectures this time, I promise," Rip said. "And I can certainly respect your wish to protect your family. But that isn't what I asked. What exactly did you expect would happen? What did you want... what were you hoping for?"

"It's like I told Jax," Leonard replied. "My father was never the best, but he never raised a hand to any of us... until after he went to prison. I thought if he was never arrested for stealing the emerald..."

"And never made any of his unsavory 'friends?'" Rip suggested.

Leonard shuddered. "That thought crossed my mind," he admitted. "But if you know anything about me, you should know that the only thing I care about more than stealing is protecting my sister." He shook his head. "But the moron still had to screw things up."

"That might have been a good thing," Rip said.

"Because I might've wiped myself out of existence?"

"That would have been the least of your worries." Rip muttered. He rubbed the bridge of his nose, trying to ward off the migraine that threatened. Getting into the mechanics of time travel with one of his teachers had always been bad enough, but situations like Leonard's went beyond anything the Time Masters had ever understood. "Look, I know you don't want to be lectured, but I just need to make sure you understand how dangerous it was to try what you did."

Leonard looked... annoyed. Was he extremely annoyed, Rip wondered, that he couldn't manage to hide it, or was Rip just finding it easier of late to interpret the man's expressions? "Go on," Leonard replied. "You were going to lecture me anyway."

Rip took a chance. "When we change time, it takes, well... time for the changes to set," he began.

"Like cement, you said."

"Right," Rip continued. "Nobody's really figured out why. This phenomenon has caused endless debates among the Time Masters—and when I say 'endless' I'm not speaking figuratively—without anyone ever coming up with a logical explanation. But one thing that we have learned is that some people, time travelers in particular, are... resistant to those changes. No matter what else happens to history, we, on this ship, would not be affected until... well, until after we've already changed things. And the part of us that is the most resistant to those changes is our memory. Which if you think of it, is a rather useful tool, if an extremely depressing one."

Leonard cocked his head. "Useful..." he mused. "I suppose... If you succeeded in saving your wife and child, but could no longer remember any timeline but the one where they survived, you wouldn't have any reason to steal the Waverider; you wouldn't know they needed saving. Or if you died in the attempt..."

"Yes, exactly. Not bad for the 'thief that time forgot.'"

"I've read a little science fiction. I understand the concept of the grandfather paradox, at least," Leonard replied. "You're saying that can't happen?"

"Not as such, no. Not so far as the Time Masters have ever determined," Rip said. "I mean, you can write yourself or your descendants out of history that way, but again, it won't catch up to you until after you've actually made the attempt—from your perspective as the time traveler." He shook his head. "To use my own mission as an example, though, the depressing part is that, though I would presumably know if I'd succeeded, I would never remember the intervening time; I would never remember the changed timeline. For me, that timeline would never have existed." Rip took a risk and sat down on the desk next to the other man. "Now, in my case, Miranda knows—knew—that I'm a Time Master. She would understand if my memories of our time together wouldn't match up with hers... even if I never told her how I remembered things. But could you imagine trying to explain to your family..."

"Why I felt like my father was the most hateful thing to walk the earth?" Leonard suggested. "Why I still grew up to be a professional thief?" He shrugged. "Might make family reunions a little awkward."

"More than that," Rip said. "Your sister might fear and hate you."

"Worth the risk," Leonard said. "If I understand what you're saying correctly, then even if I'd changed things, I would want her to be safe just as much as I do in this timeline. I'm still not getting why that would be dangerous."

"For the same reason I did not take Miss Lance up on her request to kill a certain friend of your father's before he was released from prison," Rip said.

"I didn't tell her that because I wanted her pity," Leonard growled.

"I know that. Whether you want pity or not, no one deserves to suffer like you have. When I was researching everyone's timelines, I was tempted to make a few of those changes myself."

"But you don't want to disturb history," Leonard guessed. "You don't want to risk anything that could interfere with your own rescue mission."

"In this case, I was willing to take that risk," Rip admitted. "The reason I didn't attempt to change your past is because I'd discovered you have an eidetic memory. Because you can remember most everything, even things you didn't notice the first time."

Leonard lifted one eyebrow. "I understand how an eidetic memory works," he said. "What I don't understand is why it's relevant."

"It's relevant because… because the Time Masters have precious little data on how changing history can affect someone like you. Which… which timeline you would remember. At the very least, you would retain the original version of events; changing your past, even before you joined this team and gained that theoretical protection, would not make you forget what you'd suffered. In theory, though, you might have the capacity to remember both timelines as equally real."

"And that would be dangerous, because…" Leonard prompted, his tone milder than normal. He looked away a little too quickly, but not before Rip saw the look in his eyes.

Leonard was spooked. Rip was certain this time; whatever thought had occurred to the other man had greatly disturbed him.

"I think you already know the answer to that," Rip said. "It isn't just a theory, is it? You do remember... other timelines?" He considered a moment. "Mark Mardon. When you tricked Mr. Allen and released the metahuman prisoners... that wasn't the first time you encountered him, was it?"

Leonard's eyes flashed. He sprang from the desk and only just barely avoided fleeing for the door.

In anyone else the reaction might have been nervousness, or perhaps a very mild fear, mild enough to maintain some control, anyway. But when contrasted with Leonard's usual bland manner, it could have been nothing less than the edge of panic.

"Open the door, Rip," Leonard growled. "This discussion is finished."

"No," Rip said. "This is exactly why we need to talk."

"Be careful, Captain," Gideon warned. "I'm sensing a change to his brainwaves."

"Well, obviously," Rip muttered. "He's afraid—"

"His fear is not normal," Gideon corrected. "But the change to his brainwaves is an entirely new pattern... a new personality, if you will, trying to push aside the old."

"Mr. Snart, you need to calm down," Rip said. "You need to understand... we need to understand—"

Leonard whirled around to face Rip, making the captain recoil in horror. Rip couldn't name it, but there was something seriously wrong with the other man's eyes.

"Open the goddamned door!"

"I'm sorry, but I cannot risk letting you back among the crew while you're like this." Rip kept one hand on his gun, and tried to palm a syringe with the other. If it came to it... would he be able to sedate the man before anything happened? Or would he be forced to shoot... to kill one of his crew? "You need to calm down, and I need to know what's happening to you."

"Dammit, Rip," Leonard said, shaking and panting as he tried to control whatever was happening to him. "I remember dying!" His eyes cleared, and he slumped to the floor, his fear spent and his strength with it. "Is that what you wanted to hear?" he whispered. "I remember dying."

"Oh, my god," Rip muttered. He heard the epithet echo on the other side of the door, and he shook his head. "Seems I should've had Gideon sound-proof our... discussion."

"I'm sorry, Captain."

"No, Gideon, it's my fault. I didn't expect things to progress like this. Let them in."

The door opened, and only Martin entered. "We all heard shouting," he admitted. "The others are keeping Mr. Rory... restrained. We thought it might be best to find out what was going on before allowing him to, well..." He grimaced. "I should warn both of you that Mr. Jackson is listening in on my thoughts and will tell the others if he thinks there is any trouble."

Rip nodded. "Gideon," he said, then he hesitated. "That... that other pattern?"

"Gone, captain. For the moment. Mr. Snart is still very agitated, but his brainwaves appear to have returned to normal."

"Hmm, yes, well, I'd like you to continue to monitor Mr. Snart for any similar... alterations."

"Yes, captain."

"He remembers dying?" Martin whispered.

"Just like you remember being married to Clarissa," Rip whispered back. "Even when that part of your history was temporarily, ah, broken."

"Yes, but I had a hand in changing my own history," Martin protested. "Unintentionally, of course, but..."

"Mr. Snart's case is a little more... complicated."

"Well, that's quite the understatement."

Rip crouched in front of the man huddled and shivering on the floor. "Mr. Snart? Please, help me understand. Has anything like this happened to you before? These... other memories?"

Leonard jerked his head in a nod. "Nothing near as bad," he whispered. "Little things, usually. Things I saw on the news, or somebody I'd met at Juvie, and nobody else ever seemed to remember them. I'd just assumed... well, nobody remembers things perfectly, I just figured I was imagining things, and I learned to stop talking about it. Then in 2000..." He coughed, his mouth gone dry.

Martin fetched a glass of water and the two waited while Leonard sipped at it.

Leonard had drained half the glass before he continued. "In 2000," he said, his voice gaining strength, "there was this woman... Tess, her name was. Died in some car crash. I was in jail at the time; I had absolutely no reason to know who she was. But over the next couple of years, I'd constructed this elaborate fantasy in which she'd persuaded her husband—" he gave Martin a significant look "—Doctor Harrison Wells, to hire me on for some kind of prisoner rehab program. I never thought anything was strange about it—just wishful thinking—until years later, when I'd broken into Star Labs and discovered that one of the contracts I'd imagined myself signing was identical, right down to the last comma, to the one they created for... for the people they trust with their most sensitive projects." He closed his eyes. "I could recite the entire document right now if you wanted; the professor could probably tell me if it's really the same one."

"That won't be necessary," Rip said. "I believe it's the same. What about Mardon?"

"That nightmare was one of the worst I'd ever had," Leonard admitted. "I thought I was going mad. But I can't... I don't want to remember it."

"That was no nightmare," Rip said. "Nor, I believe, was your work with Tess a fantasy." He glanced at Martin.

Martin shook his head. "Tess died in that crash because one of the Flash's enemies—a speedster from the future named Eobard Thawne—murdered Harrison Wells so he could take his place. Something about needing the particle accelerator explosion to happen at an earlier point in time, as I recall."

Rip nodded. "What you've experienced, Mr. Snart, is called a 'flash sideways.' Er... no relation to your friend Mr. Allen. Because those changes in history affected you, and because of your eidetic memory, you've managed to retain both versions of events... something that even a time traveler cannot do unless they personally experience, as a time traveler, both timelines. Something that has caused many a Time Master to go insane before we began to understand the phenomenon."

"I'm sorry, you said insane?" Martin repeated. "And yet you thought it was a good idea to bring him onto a time machine?"

"With Mr. Snart on the Waverider, I can at least monitor him if his timeline changes, and try to keep the damage to a minimum. Besides, all of the changes he described happened before he joined the crew." He turned back to Leonard. "Case in point... Mardon?"

Leonard glared at him. "You're not going to let this one go, are you? Even after I..." He shuddered.

Rip shook his head. "Given the way you just reacted, do you honestly think it's safe to just 'let this go' without trying to understand it?"

Leonard considered this for a moment, then shook his head. "So you... you don't think I've lost my mind?" He hesitated. "Yet."

"While I certainly can't blame you for being disturbed," Rip said, "for wanting to forget, I think the greater risk to your sanity lay in trying to suppress those memories without a clear understanding of just what you are trying to forget."

Leonard thought about this for a moment, drained the rest of the water in a single swallow, and nodded. "We'd been casing the Santini family for a few weeks," he began. "We planned to hit them later that day, so we met once more at this diner to go over any changes, any reason we might need to adapt the plan."

Next chapter takes place during The Flash... specifically season 1 episode Out of Time, before Barry hit the reset button.

Linked stories:
Len's memories of Tess will be covered in the prequel fic What Could Have Been... as will his reasons for being so greatly disturbed by the topic of remembering other timelines (in general; he pretty much just said why his memory of Mardon's attack specifically disturbed him).