Just a little crack!fic I came up with, previously posted on Tumblr.

What if Castle & Beckett encountered a real time machine during an investigation? Set mid-Season 7, assuming Castle was never kicked out of the precinct and became a P.I.

"But, Kate c'mon—it's a time machine. A time machine!"

Kate Beckett groaned inwardly at her husband's glee. They had been touring through the warehouse-sized storage area for the better part of an hour and it felt like every other minute she was met with a chorus of "Ohh look at this!" or "Oh my god! Awesome!"

Their victim, as it turned out, fancied himself a mad scientist (emphasis on the "mad"), and over the years had designed many a bizarre creation. As a result, they were stuck slogging through his warehouse of goodies looking for clues. Well, she was slogging. For Castle, it was Christmas morning.

"Castle, please," she begged. "Enough. You know as well as I do that time travel isn't real."

He gave her a look of utmost offense. "I most certainly do not know that. It could be real! It could totally be real!" He smiled to himself as he circled the tall, rectangular structure. "This is definitely my new favorite case."

Kate pulled her phone from her pocket and glanced at the screen to see if she had any news of the victim from Lanie. Her alerts screen was, disappointingly, empty so she dropped the device back into her pocket with a sigh. Raising her gaze, she searched the piles of junk draped in old sheets until she spotted her husband.

"Hmm," he said to himself, making another lap around the object. "I don't suppose it comes with instructions."

"You don't need them; we're going to keep looking through this junk to see if we find anything—which we probably won't," she added in a snippier tone. Truthfully, she'd given up on that at least twenty minutes earlier.

Castle gazed at her in an expression she imagined a toddler might have if he was told to leave Disney World after just half an hour. "But Becket—time machine! C'mon—where's your sense of adventure?"

"I used it all up marrying you," she replied with a smile. He gave her an annoyed glance and she chuckled to herself. Knowing the only way they could move on would be to placate him for several moments, she gazed at the structure. The large plastic rectangle was painted blue and, if she was not mistaken, vaguely resembled pictures she'd seen of Dr. Who's Tardis. Though, as she examined it from another angle, a different comparison came to the front of her mind.

"Castle!" she proclaimed with utmost irritation. "This is a port-o-potty!"

"Time machine," he corrected, his tone as firm as ever. "Get in."

She laughed. "Absolutely not."

"C'mon."

"No."

"Humor me."

She folded her arms over her chest. "Why?"

He walked up behind her and brushed his lips against her right ear. "I'll make it worth your while."

His deep tone sent a shiver down his spine. Damn, after all these years how was she powerless to resist an offer like that? He annoyed her to death and she had no doubt he was insane if he truly believed the time machine was real, but the promise of him making it worth her while once they were home, in their bed, naked beneath the sheets…

"God, fine." She grumbled. He beamed and clapped his hands together. Then, he reached out and opened the port-o-potty—er, time machine—door for her.

With a grimace, Kate stepped inside and startled when the door slammed shut behind her. Skeptical, she observed her surroundings. From the interior, it was even clearer that the plastic house in which she stood had a former life as a bathroom. Directly in front of her sat a black, boxed off area, which she knew held the waste holding tank. It appeared the toilet seat had been removed and she made a silent prayer that the other contents had been removed as well before turning to her right.

There, on the interior wall, barely visible in the dim light a black computer keyboard was mounted. Beside it, on a small white plastic hook, a gold chain dangled. Turning another ninety degrees so she faced the door, she startled at the sight of a pair of eyes. After a second she realized it was her own reflection; the port-o-potty mirror still hung on the back of the door.

"Okay, can I get out now?" she asked her husband.

"Hold on—what do you see?"

"A keypad and some sort of medallion," she responded impatiently.

"On a necklace?"

"Yeah."

"Put it on."

She reached for it but pulled her hand back quickly. What the hell was she doing? The charade was insane and, quite frankly, a little gross. "Castle…"

"Please, Kate. Just put the necklace on."

With a grumble, she reached for the chain. It was so large that it fit easily over her head. "What's with the medallion anyway?"

"It's how you get back—obviously."

Kate rolled her eyes as she dropped the chain around her neck. "Castle, I really don't-"

A strangled yell cut off Kate's thought when she was plunged into darkness. She was just about ready to yell at her husband for turning out the lights on her, when she realized he couldn't have. The port-o-potty Tardis was in the center of the warehouse and by the closeness of his voice she knew he was right outside when he spoke to her. Even if he had dead sprinted to the switch on the wall, he still wouldn't have been able to turn out the lights that quickly; not with all the crap blocking his path. So where the hell had the light gone?

Kate blinked and blinked again before slowly objects came into view. Oddly, those objects were not the keypad and blue interior wall of the port-o-potty. Instead, they were windows, picture frames, stools and a rough wooden kitchen table.

What the hell?

She must have been looking at some sort of screen on the inside of the port-o-potty, but how was that possible? And how did the details become so vivid?

Instinctually, she took a step forward and that's when she realized: she wasn't in the port-o-potty anymore; she was in an apartment. An apartment that, as she thought about it, she recognized; it was her apartment. Not the apartment she had just leased to her cousin, but the one before that; the one that had blown up. Spinning on the spot Kate muttered, "Holy shit."

From that angle she could see everything: the couch, the coffee table with all her tchotchkes, the kitchen. If this was not her actual apartment it was on hell of a good replica. "How is this possible?" she asked to no one at all.

Not a moment later, a noise from behind her roused her attention and she turned to see an ashen faced woman staring back at her. Shit! Oh shit—this was not good. This was so very not good.

Kate and the younger version of herself stared at each other unmoving for the better part of thirty seconds. Then, the younger Beckett sprang into action and charged across the room to the long table nearest the door; the table Kate knew to hold her spare gun.

"No wait!" she proclaimed. "Don't shoot me. Do not shoot me." She said, holding her hands up in a defensive stance.

Younger Beckett ignored her and pulled the weapon from its hiding place. "How the fuck did you get in here?"

"I…I…Listen, I know this is hard for you to believe, but I'm not an intruder—I'm you. Me. From the future."

The younger woman flicked the safety off on her weapon. "Nice try, psycho, but there's no such thing as time travel."

Thinking quickly on her feet, Kate held her hand a bit higher and disclosed the facts she knew she had revealed to no one. "I can prove it! You lost your virginity to a rocker named Clint and you thought it was gross because he hadn't showered recently."

She watched as the younger version of herself lowered the gun a few inches, her eyes wide with recognition. Kate lowered her hands a few inches. "Your mother was murdered when you were nineteen and even though you say you're ok with it, it really tears you up inside. You wear her ring around your neck and your father's watch on your wrist."

The woman with the gun lowered the weapon to her right side. Her arms hanging limp and her jaw open, she managed to utter out. "How…"

Kate lowered her hands and took a step closer. "I'm you."

"From when?"

Kate pulled her lower lip between her teeth. Time travel—what were the rules of time travel? She'd listened to Castle prattle on about them years earlier, but having at that point been convinced time travel was impossible, she had barely paid attention. "I don't know if I should say—aren't there things I'm not supposed to do?"

Beckett scoffed and returned her weapon to its hiding place. "How should I know?"

"No, I think there are. Like the butterfly effect or something. I can't change the future. What year is it?"

"2009," she replied, "and I don't think telling me what year you're from will change the future."

Kate let out a laugh and pushed her hands down into her pockets. Gazing around the room with awe, she shook her head, "2009? Damn I really went back, didn't I? He's never going to let me here the end of this…"

"Who?"

"Castle," she replied without thinking.

The younger woman practically growled. "Castle!? Is he still shadowing you because that is absurd! Why the hell would I-"

"Hang on let me think a minute," she said, interrupting herself. Okay, she had gone back—she had really gone back—that much was clear. But she couldn't stay. She didn't want to stay, but she couldn't. Not one second longer than she had to; she couldn't risk changing the future. Bringing her left hand up, she skimmed it across her mouth as she thought about her entry into a world six years into the past.

"What's that?"

The voice beside her startled her. The elder Kate jumped when she realized her twin self was just a foot from her. From that angle, she was able to more closely observe it. Her hair was almost shoulder length but still awkward from the short cut she'd had; damn, that really had been a bad idea. And the remnants of the maroon color? Arguably worse. She had forgotten how young she looked back then, though. Ah, the last years of her twenties; where had the time gone?

"What's what?"

Beckett reached out and grabbed onto her left hand. She held it up and said, "You're married?"

Shit. How was she supposed to respond to that? She knew her mindset back then. If her self from 2009 were to know the identity of her husband…well, that would not end well. "Oh," she said, pulling her hand back. "Yes…"

"To whom?"

Kate turned away from her, covering her wedding band with her right hand. "I can't tell you that."

The younger woman was quite for several moments before she gasped. "Oh my god! it's him isn't it? Castle."

Kate plastered on her interrogators face of stone and glanced over. "I can't say."

Throwing her hands up, the maroon-haired woman began to pace. "Unbelievable! How could you marry him?"

"I never said I was married to Castle."

Beckett stopped pacing and stabbed a pointed finger in Kate's direction. "But why else would you say 'he's never going to let me hear the end of this'? You're obviously more than a year older than me which means you're from several years into the future. Why else would he still be hanging around you—me—us!"

Kate arched a skeptical eyebrow at the younger woman; damn she was good.

As if Beckett had read her thoughts, she replied. "I'm a detective too, remember?"

Side stepping that response, Kate said, "Look, just help me figure out how to get home."

Beckett ignored the request and instead walked over to lean against the kitchen counter. Kate turned her body to face her and felt the medallion swing around her neck. The medallion! Of course! Hadn't Castle said it would be the way home?

"Did he ever finish his stupid book?"

"Castle?" Kate asked absentmindedly, her attention mostly focused on the chain around her neck. "Yeah. It was very good."

Beckett snorted and muttered something snide under her breath.

Dropping the chain from her fingertips, Kate looked up, annoyed. She really had been bitchy back then, hadn't she? "Look, I can't tell you much, but I will tell you that your husband is an amazing man. You love him very much and he loves you more than you ever thought possible."

Immediately upon hearing the words from her older and clearly wiser self, Beckett's expression softened. She pushed herself away from the counter and approached with the same curiosity and intrigue she did at crime scenes. "You look happy," she concluded softly. "I don't remember what that's like."

A sad smile crossed Kate's face. Even though she had been happy with Castle for many years, she did not forget the darkness that once fell across her life. Instead, she liked to hold on to those memories; they made her even more appreciative of her current happy life. "I know, but you will. You're not ready yet and that's ok, but when you are: don't fight it."

Beckett nodded slowly and considered this for several moments. "Should I …I mean, would you change anything?"

"No." When Beckett eyed her cautiously, Kate chuckled. "Really, I wouldn't. Everything—every moment wonderful or terrible makes us who we are and leads us to the exact right place in time; where we're meant to be."

At the level of schmaltz in her statement, Beckett rolled her eyes and concluded, "The writer told you that, didn't he?"

Kate tightened her lips in a failed attempt to hide a smile. "Maybe he did."

Her tone a little more impatient, Beckett said, "Seriously, you wouldn't change anything? Didn't anything bad happen to you—us?"

Did anything bad happen? Oh, well there was a question. If she had the choice to live her life again, she would certainly preferred to not have been shot in the chest, but even that moment came with a good one; she would not want to lose the first time she heard Castle say those three little words. Still thinking, she said, "Well, yes, but I don't know what changing that would do. If I told you to do something differently and something happened to Castle I'd-"

"HA!" Beckett interrupted her loudly, prodding her index finger in her direction. "You are married to him!"

Kate turned her eyes to the ground. Okay, that was going to be a hard secret to keep especially once her younger self noticed the ring.

"I could change that, you know. Now that I know," Beckett said pointedly.

Kate's brow wrinkled. "But why would you want to? You just said I looked happy."

Beckett shrugged. "Maybe I could be happier."

Kate was suddenly overwhelmed with the very odd desire to slap herself. "Stop being stubborn!"

"I'm not stubborn."

"You are. Look just," Kate grumbled and picked up the medallion with her right hand. "Just help me figure out how this thing works so I can get back."

Beckett stepped up close and examined it. "I don't know. Did you hold it and think about home?"

Taking a deep breath, Kate closed both hands around the medallion and shut her eyes. She thought about Castle, waking up with him in bed that morning at the loft. The warmth of his body beside hers, the soft feel of his exhaled breath against her ear. Opening her eyes one at a time she found herself still in 2009. Staring at her younger self, she shrugged.

"Well, I'm out of ideas."

"You have to call Castle," Kate concluded.

Beckett looked at her as though she'd suggested flying to the moon. "No way."

"Yes."

"No."

"Please."

"Absolutely not."

"C'mon—he'll know what to do," Kate insisted. Well, she hoped he would know what to do. He did, after all, seem well versed in this.

Beckett clicked her tongue. "At what expense? You get to leave—I'll never hear the end of it!"

Taking a step towards the younger woman, she softened her tone as much as she could. "Kate, please. I have no idea how to get back. His brain got me into this—hopefully it'll help get me back. You don't want me to be stuck here forever, do you?"

Pursing her lips together Beckett muttered, "Fine. But you cannot tell him about us in the future."

"I didn't even want to tell you," Kate pointed out to her.

Half an hour later, and with great reluctance, Beckett opened the door to the beaming, cat-who-ate-the-cream face of her writer cohort. He stepped into her apartment while saying, "Ah, Beckett remember this day! The day you called me to your apartment. The day you need my assistan…" His voice drifted off when he found they were not alone in the apartment. Instead, in the center of the room, he spotted a remarkably familiar looking woman.

Castle stood, dumbfounded before slowly rotating his body towards his partner, still standing beside her apartment door. Yep, she was definitely right there, within arm's reach of him. But then…how was she also standing across the room? And with different color hair? Perplexed, he took several more steps into the room.

"Ah, Beckett, you never told me you had a sister…"

Beckett shut the door and joined her time traveling companion. "I don't have any siblings, you know that."

Castle took a few steps towards the two women, suddenly convinced his mind was playing tricks on him. "Cousin?" he guessed hopefully.

"I have cousins, but she's not one of them."

"Then…wha…" His voice drifted off as his eyes jumped between the women. Same eyes. Same nose. Same agonizingly stunning cheekbones and pink lips. They were identical. They were the same person. There were two Becketts! But how was that even possible. How did that—

Castle let out a loud gasp and clapped his hands over his mouth. Glancing between them, his eyes welling with tears of joy he proclaimed, "Time travel is real! It's real! Best day ever!"

"Calm down, Castle," the older woman told him. She didn't even bother hiding the smile that crossed his face, knowing how much he would love this news. It was even more fun to see on his lighter, more youthful face. As she had seen him every day, she hardly noticed the lines that appeared, but now with his younger self in front of her, they were plain. She didn't mind, though; they made him more distinguished. They made him her Castle.

Castle's eyes widened at the elder woman. Her voice was familiar, but it sounded so odd coming out of someone he didn't quite recognize. Though it stuck him as bizarre at first, he got over it quickly. "Nope! This is amazing! This is awesome!"

He began circling the older woman, taking her in from every angle. "Where did you come from? How did you get here? What year is it where you're at? What's going on? Have the alien invasions started yet?"

"Castle…"

"Down boy," Beckett told him. "She's not too into answering questions."

Wisely, Kate replied, "I can't tell you anything, Castle—you should know that."

He nodded and skimmed his fingertips over his chin. "Right, right you can't alter the past or risk changing your future. Ooh this is just so exciting!" He bounced up on the balls of his feet. "Where are you going to go next? You can travel forward and back, right?"

Kate let out a laugh and shook her head. "Honestly? I have no idea. You're the one that talked me into this whole thing—that's why I had her call you."

Castle's eyes widened. "Me!?"

"Yes. You talked me into the time machine—an incident I'm deeply regretting at present," she added with a grumble.

Castle continued to stroke his chin as he observed her. "So…in your future I'm there. Interesting; that's interesting. Am I correct in assuming this has something to do with a case?"

"Not exactly."

His chest fell and his shoulders slumped so he quickly resembled a deflated balloon. "Ohh…no time traveling killer?"

She smiled at him one of her perfected Crazy-Castle-Theory smiles. "Sorry, Castle. Not yet."

Rejuvenated by a new idea, he stood up a bit straighter. "But how do you know? Maybe I just solved your case—from the past! Oh my god, I really am the best partner ever!"

Both Kates rolled their eyes and proclaimed, "Castle focus!"

Castle took a step back and laughed. "Oooh that was freaky!"

The elder Kate added in a softer tone. "Please?" She picked up the medallion from around her neck and said, "I just need you to-"

"Hey wait," he reached out and picked up her left hand. Damn it! Why hadn't she remembered to take of the ring while they were waiting for him to arrive?

A gleeful expression on his face, Castle held out the ring-bearing left hand to his coworker. "Oooo Beckett you're married."

Beckett dismissed this thought with the flick of her wrist hand. "Yes, we've already covered this."

"I haven't covered this," he pointed out. Then, he turned to the elder Kate. "Who's the guy?"

She gave him an annoyed look. "You know I'm not going to tell you."

"Doesn't mean I can't guess." He dropped her hand and began to pace the space in front of the identical women. "Okay so…let's see here. I'd say you're from about…" He paused to look her over. "Oh, five years into the future. Five years… and how long have you been married?"

"Not telling you."

He gave her his classic 'Why are you ruining my fun?' expression. "Oh c'mon—where's the harm in that? More or less than two years?"

"Less," she admitted reluctantly.

"Okay. Okay…so you get married no less than three years from now, possibly up to four. You're not exactly the runaway Vegas marriage type so that means you probably already know the guy. Or you're just about to meet him. Ohh! How fun would that be Beckett?" he turned to the younger woman with a grin. "If we knew when you were going to meet him?"

Deciding to deflect the conversation away from dangerous territory, Kate said, "Castle, can we just-"

"OR!" he proclaimed, ignoring her completely, "Or what if you already know him? It could be someone I know! Ryan or Esposito…"

"I did not marry Ryan or Esposito!" Kate said immediately.

Castle winked at her. "Thanks for narrowing down our suspect pool. Now what about-"

"Castle!" Beckett snapped. "I did not invite you here to play The Dating Game—now would you just help her already."

He blinked, befuddled. "Help her with what?"

"Going home. She can't figure out how to get back." When Castle turned his back to her, Beckett shot her older self an expression that clearly said, "I cannot believe we married him." Kate fought a laugh, though she couldn't exactly disagree. Castle from the year 2009 was quite different than the one she married.

"Okay, okay," Castle began, gathering his thoughts. "How did you get here?"

Kate held up the medallion for him to see. "I think it has something to do with this."

"You put on the necklace?" he asked; she bobbed her head. "And what were you thinking at that time?"

"That I don't know who is a bigger idiot: you for talking me into this time machine or me for agreeing."

Beckett snorted with laughter and the other two occupants of the room looked at her until she straightened he repression.

Turning back to the elder woman, Castle said, "Very funny, Beckett. Future Beckett?" he questioned with a brow raised. Then he shrugged. "What else were you thinking?"

Kate thought back to that moment in the port-o-potty time machine. "I guess…I guess I might have thought that years ago I wouldn't have believed in this."

The writer beamed. "Ahh now we're getting somewhere. So I think all you have to do is hold the necklace and think about your present life."

"Should she put on red slippers and click her heels together too?" came a snarky response from across the room.

With a perturbed expression, Castle turned to face his partner. "You know what? I'm glad we got to meet her because she seems like a lot more fun than you. That means there's still hope for you, Detective."

Slightly miffed, Beckett tightened her lips. "We're the same person."

"No, you're not," he corrected. He stepped around behind the older woman and used his right hand to gesture at her features as he named them. "Look at her: soft hair, sparkling eyes, arms down at her sides instead of so tight across her chest she's trying to break her own ribcage." At the mention of this, Beckett dropped her arms, though her face remained taunt.

"Don't be too hard on her, Castle." Kate told him gently.

He turned to her and smiled. "I won't; I promise. Now, let's examine this necklace. I don't want to touch it, just in case, but look at it all over. The sides, the front." He slid his hands into his pocket to prevent accidental touching, and lowered his head to examine the medallion as she flipped it over in her hands.

"What am I looking for?"

"Something to press – a button, a groove…"

"Oh!" Kate gasped when she found a small button along the outer edge of the object. It was barely a few millimeters long and not raised off the surface of the object; no wonder she hadn't spotted it before!

Seeing what she pointed out to him, the writer nodded. "Yeah, yeah that should be it. Now, when you press it just remember to clear your mind and think of nothing else but the exact moment you left your time. Then you should be back where you started."

Kate smiled up at him, never more thankful that he was able to help right her inadvertent time travels. "Thanks Castle." Then, turning to her sulking doppelganger, she said, "Goodbye Kate."

Startled at the mention of her name, she glanced up. "Wha? Oh yeah…bye."

Kate turned back to the writer standing beside her and offered him a soft smile. Just before she could open her lips to thank him again, he leaned his face in closer to hers and said in a voice barely above a whisper, "By the way, I know I'm the one you married."

Her jaw dropped an inch "Wha-"

He rocked back on his heels with an easy expression. "Please, Kate—you've always been powerless to resist me."

She shot him an annoyed look and he laughed. "Don't worry; I won't tell her. Though," he added, lowering his face closer to hers. "I don't suppose you'd tell me how long I have to wait before—"

"Now where would the fun be in that?" she retorted. Then, after thanking him once more she pressed the button on the medallion and shut her eyes. When she opened them again, she came face to face with the interior of the port-o-potty. Thank god!

Out of sheer desperation to never leave her current time period again, Kate whipped the medallion off her neck, tossed it aside and burst out of the port-o-potty nearly running smack into her husband.

"Kate! Oh my god!" He proclaimed, pulling her immediately into a hug. "Don't do that to me!"

"Do what?"

"You weren't saying anything and I couldn't get the door open. I was really worried that-"

"Wait…how long?" she asked, a curious eyebrow raised.

"I dunno a minute or two? But it was really freaking me out because-"

"A minute? I definitely gone at least an hour," she said, more thinking out loud.

Castle's brow wrinkled. "Gone? What do you mean go—did you go? Did you travel?! Oh my god its real! It works!" he proclaimed, clapping his hands and bouncing on his toes. Kate could not help but smile at the similar reaction she was re-living. Suddenly, he sopped bouncing and his face straightened. "Wait, oh god you didn't change anything did you? Who did you see? What did you touch?"

"I saw us," she informed him.

"Us?"

"Yes, I landed in my apartment six years ago and I saw myself and you…doesn't that mean I should remember seeing myself. I mean, I remember seeing myself because I just saw myself but shouldn't I remember seeing myself in the past? And what about you? Wouldn't you remember? Isn't that how Back to the Future worked?" Suddenly, her head was beginning to hurt. That was one hell of a confusing thing to think about!

Castle shook his head as he thought. "No, Marty and Doc never revealed themselves as themselves; they had different identities. You and I would have obviously recognized you but I don't remember seeing you…"

Kate thought for a moment. "Well, maybe you didn't."

"Huh?"

Smiling at her husband's dumbfounded reaction, she said, "Well, in the past, you told me to think about the exact moment I left this time. If I left and returned the same moment, doesn't that mean I never went at all?"

His eyes widened at her explanation. "Interesting." What she was saying could make sense, but he definitely wanted a firsthand account. "Okay, my turn."

Kate grabbed his arm before he could open the time traveling door. "No, Castle—it's dangerous."

He whined immediately. "But!"

She placed both hands on his arm and softened her expression. "Please don't. I don't want to risk losing you."

Staring down into the eyes of his wife, Castle could not help but agree to her request. He wanted to experience time travel, but not at the expense of upsetting her; he loved her too much for that. "Alright, okay. But promise me when they open up the time traveling theme park rides you'll let me buy the very expensive up front tickets so I can have one of the first trips."

"The…what!?" she responded as she stared at her husband, completely befuddled.

"Well, you know, now that this technology exists, people are going to-"

"No, Castle. We can't let anyone know about this. Can you imagine how dangerous that would be? Someone could go back in time, change things, and then create a chain of events that leads to you not being born. Or me not being born."

He dropped his chin, realizing she was right. "Yeah, okay…but then you have to tell me what it was like—every single detail!"

"Deal," she said with a laugh.