A/N: Speaking of Fringe, holy Lance Reddick on Castle, Batman!

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"Are you kidding?" Beckett hissed at Gates, toeing the line between discontent and insubordination. "You want me to take care of him for the night?"

"Sounds good to me," Rick grinned, letting his eyes wander just enough to make his meaning clear. As if it weren't already.

"Dude."

"No."

Castle and Beckett spoke at the same time, and shared a relieved look. They were sickeningly in sync.

"Yes," Gates pressed on. "The man hasn't done anything wrong. He hasn't broken any laws, he hasn't threatened anyone. Other than the multitude of borderline lewd comments, he hasn't even bothered anyone."

"He bothers me," Castle supplied.

"Welcome to my world, Mr. Castle."

Castle had the good sense to look sheepish, but Rick couldn't stop grinning. This was hilarious. Even being cuffed to the desk, this was hilarious.

"Sir," Beckett began again. But Gates held up a hand to stop her. She popped open a bottle of aspirin for at least the third time in as many hours and tossed back two more, without even any water to help them down.

"Detective, if you can think of a reason to keep him in lockup, I'll do it."

There was a long pause while Beckett thought hard and stared at the imposter.

"He's impersonating an officer."

"That guy," Rick noted, "is not an officer."

Gates raised both eyebrows and lifted her shoulders. "He's right. And frankly, we don't have any evidence that he's impersonating anyone. If you want to set him free go ahead, but I think you'd do better to keep an eye on him."

Beckett stood stock still as her captain walked away, and looked at Castle. "What do you think?"

"Actually," Castle stuffed his hands in his pockets, "I think it's kind of cool. Terrifying, but cool."

"Yes!" Rick tried to stand but his cuffs pulled him back to a sitting position. "Terrifying, but awesome. Just what I was thinking."

Castle looked at him with surprise and then turned back to Beckett. "C'mon, Beckett. Can we keep him?"

Beckett rolled her eyes at him, then looked down at Rick. "Well, he is pretty cute."

Rick winked at her, and Castle frowned at him. "Maybe... let's not keep him. Let's try to get him back to his universe as quickly as possible."

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"Listen, do you have any ideas about how to get home, Castle? Well. Alt-Castle? New Castle? I can call you Newcastle," Beckett trailed off, having lost her train of thought in the insanity. She focused on her driving to clear her head of the confusion.

"Call me Rick," he replied, and smiled to himself. How many women had he said that to over the years?

"Noooooooo," Castle moaned, covering his face with his hands. "She can't call you Rick."

"Why not? It's my name." Rick leaned forward to rest his hands on the cruiser's shoulder rests from his spot in the back seat and poked his head between Beckett and Castle. "I'd like to hear her say my name." When Beckett gave him an exasperated look, he grinned at her, twinkling eyes highlighted by the scruff on his face. Beckett's face flushed, just barely visible from his location right behind her, and she turned away to hide a smile.

Castle peeked out from between his fingers and caught him staring at her, still grinning. "Hey! Don't do that!" the other man yelped and swatted at his face until Rick was forced to duck away and lean back in his seat. Castle turned all the way around to glare at him, his expression saying things he probably didn't want Beckett to hear. She's mine. Hands off. Get your own Beckett.

He may not have said it out loud, but Beckett seemed to have heard him anyway. "Babe, we're okay," she murmured, for Castle's ears but there were no secrets in the quiet sedan. And either way, Rick could see her reach over to tangle her fingers with Castle's. How quaint.

"I only call him Rick when I'm upset," she spoke to Rick again, meeting his eye in the rear-view mirror. "The worst moments between us."

Castle glanced over at her. "And the best." He waggled his eyebrows, his jealousy having dissipated at her touch, then turned around again. "She also calls me Rick when-"

"Hey, no." Beckett interrupted and untangled their fingers with a shake of her wrist, like she was shaking off the words, and sighed loudly. "This is already weird enough. He doesn't need to think about when I... When I call you Rick."

Castle grinned at him with a challenge in his eyes for another beat before settling back in his seat. Rick smirked and looked back out the window, taking in the scenery. So familiar, yet worlds apart. "Hey, I didn't think to ask. You live at Broome and Crosby?"

"Yeah," Castle answered, pointing at the building on the corner. "Penthouse."

"Awesome. All the comforts of home." Still staring out the window, he finally realized why the streets looked strange. "You know, where I come from most of the road markings are yellow, not white."

Castle turned around again, with gleeful interest. "Really? What else is different?"

"You mean other than that in my world there isn't another version of me already living my life but having less fun? Well, I already mentioned that those silly button-all-the-way-to-your-chin blouses aren't in fashion. Thank God." He felt the right side of his mouth creep up in a smirk when he could see Beckett run a hand absently over her shirt.

"Well," Castle laughed, "they aren't really in fashion here, either."

Beckett, having just parked the cruiser, slammed the vehicle into park and turned a scowling face to her partner. "Seriously?"

"Oh, no, Kate, I meant... I meant..." Castle stumbled, but Rick's laughing interrupted him.

He slapped a hand down on his knee and rocked back with his hilarity. What a dufus to say something like that. What a dumb dumb. A plaid-wearing, clean-shaven dufus who follows this super-hot detective around like a puppy just to annoy her when she is clearly so willing to be seduced.

"Oh, man," he wheezes, struggling to control himself. "That's good to hear. If I get caught in this world it would be such a bummer to deal with all those buttons!"

The driver's side door slammed shut when Kate... Beckett got out and stalked across the garage. "Uh, give us one second," Castle mumbled before he flailed free of his seatbelt and followed her out. Rick waited for ten whole seconds before following them. Plenty of time for privacy later, he figured. Snippets of Beckett's angry words and Castle's soothing undertones made their way to him as he stretched beside the car, feigning disinterest.

"I wish you'd just said something," Beckett ground out from between clenched teeth. Her arms were crossed defensively, and when Castle reached out to touch her she stepped away. "I mean, if you think what I'm wearing is ugly you might as well tell me so I can prevent myself the embarrassment of walking around-"

She might have gone on, but this time Castle snagged her arm and cupped a hand to her cheek despite her efforts to avoid him.

"Kate," he murmured, and suddenly Rick felt like he was intruding. Something more than a poor choice in outfits was passing between them, and he felt like a voyeur. But it was entrancing, watching this other-him and this other-Kate interact, like a window into his future. So he watched, and listened.

"Kate, you're beautiful no matter what you wear."

Beckett rolled her eyes and huffed. "Even when I wear this ugly shirt. All of these ugly shirts that I have that look just like this."

"They're not ugly. They're... conservative."

Rick choked down a laugh, not wanting to interrupt.

"You haven't always worn them. But that guy," Castle gestured over toward Rick. His eyes widened in annoyance when he discovered him watching unashamedly, and he flipped a hand at him. Go away. Yeah, right. "That guy," Castle growled, "he doesn't know why you started wearing them. He doesn't know you. I know you."

Rick watched curiously as the cryptic words seemed to work some kind of magic and Beckett finally looked at Castle. "I didn't know you noticed."

"Of course I did. After you were shot I-"

"You were shot?" Rick asked in wonder, forgetting for a moment to pretend he wasn't listening. Castle glared again and Beckett looked over in surprise, as if she'd forgotten he was still there. "Where?"

Beckett stepped away from Castle and tugged self-consciously at her top. "At Arlington," she replied, avoiding eye contact, but he watched with a surprisingly heartfelt pang as she pressed the heel of one hand against the center of her chest. But what she unconsciously indicated seemed impossible, who could survive that? Beckett dropped her hand and tipped her head toward the doorway behind her. "Come on, Rick'n'Castle. Let's go up."

Rick followed a step behind as they entered the loft, preparing himself for the shock of seeing his own loft lived in by different people. But when he looked around, he realized that only the bare bones were the same. The loft was decorated differently. There were no gauche Martha touches, and yet the place seemed homier in general. A little more lived in, a little more loved.

"Huh," he said, absently brushing his bangs down as he looked around. Castle and Beckett were dropping things in the kitchen and reaching immediately for wine, but Rick stood rooted near the doorway. He felt like he'd stepped into the Twilight Zone. "So," he called, hesitantly, "is Mother... Mother doesn't live here?"

"Oh, she does," Castle responded as he filled a wine glass for each of them. "Hurricane Martha will be blowing through some time tonight. Alexis, too."

"Oh, she's in town?"

"She lives here. Well, she goes to Columbia, but mostly she lives here."

"Huh."

Suddenly some of the fun of this situation was draining away. This wasn't home, no matter what it looked like. Beckett approached him slowly and offered him his share of the wine with a sympathetic smile. "This all sinking in?"

"Yeah." He looked at the glass in his hand. "Actually, do you have any whiskey?"

"We do, come on." She grabbed his hand for an instant, habit and familiarity confusing her logic, but let it go right away.

He grinned at her cheekily and leaned closer so he could speak softly into her hair. "You know, once he's asleep, if you want to have a good time... HEY! OW!" Rick ducked and grappled at his ear, which she had caught in a vice grip.

"I was trying to be nice," she barked at him, twisting the surely damaged cartilage of his ear until he was bent over and spinning to try to ease up the pressure.

"Peaches! PEACHES!"

The pain stopped immediately, and he straightened slowly, rubbing the side of his head where he hoped his ear was still attached. He couldn't really feel it anymore.

"Peaches?" Castle asked as he approached. "Pretty soft, dude." Beckett lifted an eyebrow at him, but said nothing. "Oh, let me guess," Castle continued, "you like peaches, right Beckett?"

"What?"

"Oh don't deny it," Castle griped, "you've been flirting with him since he arrived."

"You're kidding, right?"

"No! I saw you blushing in the car and twirling your hair at the precinct. You like him."

"He's a jerk!" Beckett jabbed a finger in his direction, then balled her fists at her side as she glared up at him. "And now you're being one!"

Rick turned and started to argue that he wasn't a jerk, but shrugged and wandered away from the bickering couple. Their voices followed him, but he focused on the bookshelf in front of him. He picked up a book that this Castle had apparently written, Heat Wave, and flipped it over to read the superlatives on the back.

This thing was a hit. He flipped the first page open and read a few paragraphs, and then he got it. He looked up, grinning, and walked back over to Beckett and Castle who were standing nose to nose while they argued.

"Well if you had just told me that you thought I looked like an old spinster librarian before this guy arrived-"

"Oh. My. God. Kate, I never said-"

"Hey," Rick waved the book at them to interrupt the tirade. "Are you Nikki Heat?"

He thought they would laugh about it, that she might blush and smile and admit to it. Instead, the detective groaned loudly, smacked her Castle soundly in the chest and threw both of her hands out in a gesture of long-suffered frustration. Wine sloshed dangerously in her glass, but remained contained, even when she stomped back to the kitchen.

Castle looked at Rick with a hangdog expression, and sighed. "You had to bring that up, did you?"

"I thought she must have been flattered."

"You'd think, wouldn't you?" He didn't wait for an answer, though, and followed Beckett into the kitchen. Rick, not knowing what else to do, plopped down onto the couch and flipped open the Nikki Heat novel again. He might as well get his own inspiration in case he ever got home.

He'd only read a page or two, sometimes lowering the book to listen to the continued bickering from the host couple, when the sound of a key turning in the lock caught his attention. Somehow, the other two heard it too, and when the door opened Beckett had one Castle on each side of her and an expectant grimace on her face.

Martha and Alexis entered in a flurry of chatter and shopping bags, and Rick had enough time to feel a heartwarming little thud when he saw Alexis. This one hadn't gone Goth. Then they looked over at their welcoming crowd, and froze. Then all kinds of chaos broke loose.

They screamed in unison, Alexis' hands flying to her cheeks and Martha advancing with her bright orange purse raised as a weapon. Castle jumped over and took hold of her purse before she could attempt to do any real harm with it.

"Hey!" "No, Martha..." "Mother, no, it's alright..." Their voices fell all over each other and they stumbled to a halt, staring quietly until Martha spoke up.

"Richard Castle, what is going on here? I can't even imagine..."

"I can't even," Alexis repeated, eyes as wide as saucers as they bounced back and forth between the doppelgangers.

Beckett sucked her lower lip into her mouth and walked over. She handed a stunned Martha her own wine glass before plucking Castle's out of his grip and handing it to Alexis. They each took a sip without thinking, and Beckett took the opportunity to try to explain.

"Hey, guys. Look, this is going to sound crazy. Maybe it is crazy, the jury is still out. But this other Castle, as far as we can tell, well, he's from another universe, and he's going to be staying here tonight." She clasped her hands in front of her and waited.

Alexis set her glass down with a thud, spilling some over the edge. She stared at Beckett, searching for some evidence of a joke, and found none. Martha, on the other hand, looked each of them in the eye, downed her entire glass in three big gulps, and wiped her mouth with a gloved hand.

"This is terrible," she said finally. "Just terrible."

Castle frowned. "You know, I'm beginning to think you guys don't like me as much as you say you do."

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A/N: Thanks for reading! One more part, though I'll probably update He's Armed before I put the last bit of this out. I'd love to know what you think!