A/N: I should be working on Untouchable, my longer Castle fic that has started to take on a life of it's own, but this came to me and I thought it would be fun to share. Set after "Belly of the Beast" but not a direct post-ep.

I don't own them, but that's not a secret. ;)

Cosmology

-n

The investigation of the origin, structure, and development of the universe.

Martha may have had the right idea when she told them to go to city hall.

They had a song and he had let her have her choice of font on the save the date card, but those were the only decisions they had made so far. Tonight alone Kate had already vetoed the full orchestral arrangement and the life-size ice sculptures of the two of them.

His money was never exactly a point of contention, but she was a practical and self-sufficient woman. Excess had always been a turn off. Castle was different. Going overboard was pretty much his baseline. He enjoyed spoiling the people he cared about, and she while couldn't begrudge him that, she often struggled to be comfortable with it. She wouldn't let him get away with it in this instance. He had started by suggesting they wed in space, and had only reigned himself in slightly since then.

"Castle, we aren't buying trained doves to carry my train," she told him exasperated.

"But with this one they'll also release a set that will drop confetti over our guests after we say 'I do'!" He still had his finger on his laptop screen, the bed shaking a little as he bounced with enthusiasm, his eyes wide with excitement as he pointed out the ridiculous wedding package.

Closing her dog-eared copy of Heat Rises she flopped back down on to her pillows with a sigh. He clearly wasn't going to let her get any reading done. Gathering her patience she turned to face him, propping herself up again on an elbow. She arched a skeptical eyebrow "Confetti?"

"Biodegradable confetti," he clarified. Her ability to read him out shined everyone's, but there were still times, like last Thanksgiving, where it was a mystery as to whether he was teasing. Tonight it was irritating her. Moreover, it annoyed her even more that a part of her liked that it irritated her. She was so hopelessly in love with him that sometimes it really pissed her off.

"No birds or confetti," she said. When he opened his mouth to protest she gently swatted her palm over his face and held it there. "No trained animals of any kind," she told him firmly. He nodded his understanding and she took her hand off his head.

"Look, they have a superhero package!" He ducked her hand this time when she tried to silence him again.

"No, Castle."

She tried to grasp on to her annoyance, but she felt the pull of him, the gravitational force that left her helpless but to engage him. She caught the mischief in his eyes and only ended up scooting closer.

"But they'll set it up so you can lasso your arch nemesis in front of everyone," he defended.

She quirked an eyebrow, "We're inviting Senator Bracken to our wedding now?"

He shrugged. "Well, we don't have a mailing address for 3XK. Plus, he'd probably want to bring a date."

"I also think he's technically your arch nemesis anyway," she said, running her fingers lightly over his bare forearm.

"Yes, but we're getting married. What's mine is yours and all that. We'll have to combine our rogues gallery now." He closed the laptop and slipped it onto his nightstand.

"What like Green Arrow and Black Canary?" she asked. Her hand made its way across his shoulder and settled over his heart. She massaged the spot gently, and smiled when she heard the slight hitch in his breathing.

"That might be the hottest thing you've ever said," he growled pulling her to him. A near foreign sound escaped her as she landed on top of him, to her own ears it sounded suspiciously like a giggle. Damn him. "They're a much better comparison to us than Batman and Elektra. Plus, you'd look so incredibly hot in fishnets," he added as he nuzzled her.

"I'll wear the fishnets if you get into a pair of green leather pants."

"Deal!"

"We're not having a comic book wedding," she breathed against his mouth, her voice sultry and low. A strangled cough escaped his throat as she adjusted herself so that she straddled him.

"You're right. That's a terrible idea," he quickly conceited. She leaned down and placed a long kiss on the small part of his sternum his t-shirt didn't cover. She kept going, trailing her way up to his Adam's apple.

"Glad you see it my way."

"I'm just trying," he closed his eyes almost losing his words, as she nipped at his skin, "to narrow down our options here Beckett." He tilted his head back to give her better access to his throat. Her advantage over him began slipping as his days' worth of stubble and the faded musky smell of his cologne began hypnotizing her.

"Can we narrow to something other than the ridiculous and the extravagant?" she scolded gently, her fingers teasing the hem of his shirt.

A small gasp escaped her as his hands slid onto her abdomen and began gently popping open the buttons of her night-shirt. She shivered as his palms moved up her rib cage, warm and firm, and unrelenting. The room was feeling a lot warmer.

"Well it's process of elimination isn't it?" he argued lightly into her ear. It tickled and a surge of heat spun within her. "You won't dish on your dream nuptials, so we're going to go through everything until I figure out exactly what you want. I'll lasso the moon if you want it."

"Did you just turn a Wonder Woman reference into an It's a Wonderful Life reference?"

"What can I say. I'm just that good."

She still marveled at how easily this went for them. In the beginning she worried that they would fizzle out, that their passion would blaze like those old magnesium flash bulbs, hot and bright and over in a blink. She knew better now. What they shared burned so consistently and so brilliant it should probably have been given it's own stellar category. They knew each other so thoroughly, and where in such perfect orbit that incredible was their starting point.

"I told you, simple is fine," she pulled his shirt over his head and tossed it aside. She was surprised to find his expression sober by the time she was done.

"I don't want you to settle," he said seriously. There was concern edging his expression that melted her.

She pressed her lips to his eyelids, his chin and forehead. Edging her fingers along the sides of his face she tilted his head so that they were eye to eye. She had always meant what she had said their first night together.

"I just want you," she told him.

He shivered and rubbed his thumbs lightly on her elbows as they parted, and she forced herself not to shy away from the devotion in his gaze.

"I mean it. If there's anything you want in this, anything it all, I hope you'll tell me."

She got the uneasy feeling that he wasn't just talking about their wedding anymore. Still, she promised a soft, "I will," into his mouth.

"I want you to have everything."

She kissed him again and spent the next hour assuring him she already did.

"I think-" Castle panted heavily. "That I need," he breathed in again, "to do more cardio," he inhaled deep, "before our honeymoon."

"Don't sell yourself short, Babe. I've always admired your stamina."

She rested her forehead in the crook of his neck. Her breathing was evening out faster than his, but her heart was still pumping violently. He pulled the sheets up and the cool cotton was a nice respite from the heat radiating off their bodies. Utter contentment flowed through her.

In the weeks since that terrible night at Vulcan Simmons' compound she had tried to keep the promise she had written to Castle when she thought she might not make it. She hadn't told him about the letter, he was already haunted enough by her brush with death and she didn't need to pour fuel on the fire, but she had tried to express herself to him as well as she had on that paper. Somewhere along the line he became her whole universe, and she needed him to know.

The week after the failed narco op Kate had, for the first time, called Dr. Burke in front of Rick, and did not step into the bedroom to phone as usual. It was her little way of showing him, letting him know that she had destroyed the very last walls between them.

They weren't really walls if she were being honest, hadn't been since she accepted his ring. They were more like paper screens, designed to shield off the facets of her he knew were there, but that she wanted to pretend were still a secret. She had torn them down for him, or they had burned up in the atmosphere of the engagement. Either way, she trusted in what she and Castle had enough to put her ugly parts in full view.

"I love you," she said against his shoulder. "I don't say it enough. It took me too long to say it in the first place."

"You tell me enough," he reassured her. His hand slipped playfully to her ass then, "You could show me more though."

She laughed despite herself. "I've condemned myself to a lifetime of cheap come-ons haven't I?"

"The cheapest," he said proudly.

Kissing him again, the warmth in her chest spread, humming through her pleasantly. It just felt so good to love him, even better to be loved by him, her silly writer, who would give her the world if he could. It made her once heavy soul weightless.

"I love you," she said again. The words began pouring out of her and she pressed her mouth to his after every sentence. "I love your stupid pick-up lines. I love how you see the world. I love that you believe in the impossible even when I can't. I love that you've made me a better stronger woman. And I love that you never gave up on us when I was too scared of this to try."

He looked at her in a way that always made her blush, awe written on to his features as if she were some sort of rare celestial occurrence. His very own shooting star.

"I don't deserve you," he said, his eyes shifting to something uncertain, as if he was waiting for her to agree.

Well then, she would have to shut that down before it began. "Don't," she said leaning in to nip at the tip of his nose. "We sound ridiculous when we start with that. I used to be so afraid I wasn't worthy of your love. Castle, even my therapist got tired of hearing it. We deserve to be happy don't you think?"

He nodded his agreement.

"Then we deserve each other. I know I'm happy, and while I'm going completely off circumstantial evidence here," she ran her hands along his shoulder and the beads of sweat that had collected during their exertion, "I think I make you plenty happy too."

The wedding planning would have to resume another night. His smile was bright, and broad, and just a little bit predatory.

"The happiest."

End.

A/N: Let me know what you thought. I'm a comments-aholic. Also, as per usual I apologize for my comma usage. ;)