Disclaimer: I don't own Castle or any of the characters.

A/N: There really aren't any spoilers in here, just what I know from the summary of episode 10 and what promo pictures have come out. Most of this is just purely what I would like to happen when the two take care of a baby. I typed this up without really meaning to so I hope you like it.

"How is he?" a voice behind Kate asked. She wheeled around and saw Castle standing inside the doorway to the guest bedroom, arms crossed over his chest.

She turned back to stare down at the infant who was currently sound asleep in his crib. A soft smile dawned upon her face. "He's just fine," she replied quietly so as not to wake him. She rested her forearms on the crib railings and relaxed.

Castle joined her by the crib and placed a hand on the small of Kate's back. It was well past midnight and when he'd woken up to an empty bed, Castle had gone in search of his fiancée, guessing correctly where she'd be.

It hadn't taken long for Kate to become accustomed to taking care of the small child that wasn't even theirs. The baby boy had been carried to a church by a mysterious man, who wasn't his father, and then the man died. He'd been murdered. As part of the investigation, Beckett, and by extension Castle, had been ordered to care for the boy to ensure that no harm came to him until they could find his connection to the murdered man and then his real parents, if any were still alive. They didn't even know the child's name and thus had to create one themselves.

"Let's call him Jameson," Castle had told her enthusiastically.

"No, we're not naming the kid after a character from your books, Castle," she'd said sternly.

"Why not? It's a great name."

"It's a pretentious name," she'd retorted. "And that's just weird. The character you based off me has sex with the character you based off you and now you want to name the boy after said male character? I don't think so."

Castle had made a face. "Yeah, I guess you're right. That is kind of strange." He'd thought for a moment before saying, "Okay, what about Alex?"

"Too close to your daughter's name," she'd fired back.

"Frank?"

Kate looked unimpressed. "Does 'Frank' really sound like a baby's name to you?"

"What about Tommy, Matthew, David, Daniel?" He paused then exclaimed, "Oh I know: Spartacus!"

She looked at him like he was crazy. "Castle, how the hell do you go from Daniel to Spartacus. On another note, who the hell would even name their child that?"

"Apparently Spartacus's mother would," he told her smugly.

"Yeah, well, that was about 2000 years ago," she said dryly. "What about Lucas? Or Luke for short," Kate had suggested.

Castle had mulled it over for a minute, tossing it around in his head. Finally he had nodded, and said, "Luke it is, then."

Now here they were, standing beside the crib that Castle had bought at a store and assembled rapidly, watching the little boy sleep on his back.

Kate felt the compulsion to touch him so she did. She reached out a hand and ran a finger softly over the sleeping child's cheek. "He's nothing like I'd expected, Castle," she commented quietly.

"I know," he replied. "Even I expected sleepless nights and horrible tantrums and fits. Never would I've thought he'd be one to sleep like a rock at night." The writer watched as his fiancée ran a hand gently down Luke's back that was rising and falling continuously due to his breathing. He gazed lovingly at her and couldn't help but think that she'd make an amazing mom one day. First, though, they needed to have that talk before any kids actually did pop up.

Nudging her lightly, Castle said, "Come on, Kate. Let's go back to bed."

She shook her head. "I can't, Castle. I just can't bring myself to leave him."

"You know he'll still be here when we wake up in the morning, right?"

"Well duh, but I…." she trailed off.

Castle wrapped an arm around her waist. "That's just your maternal instinct, Beckett. You see a small child and you immediately want to care for and protect him. That's why you're basically refusing to leave his crib tonight even though we both know you need sleep."

She hummed her response and was then silent for several moments. Suddenly, she looked at him and spoke. "Will it be like this? When we have kids?"

Castle looked at her, startled. He definitely hadn't expected her to be the one to say anything about potential future kids.

Misreading his surprise as a bad thing, she tried to backpedal. "That is, if you even want kids. I know you already have a grown daughter so it's okay if—"

"Kate," he interrupted. "I would love to have kids with you one day, don't get me wrong. You just surprised me and that's why I sort of jumped like that."

There was wariness in her eyes. "So, even though you have Alexis, you'd still want to raise another child?"

"Of course." He turned his body to face her, grabbing one of her hands. "I've always wanted more than one kid, but recently the only person I want to mother them is you, Kate."

She smiled sheepishly. "I'd kind of like that too. You're the only man I could ever see myself having children with, Castle. But…I'm nowhere near ready for them."

"And that's okay," he told her. "Let's focus on actually getting married first before you start popping out six kids."

"Six?" she asked with disbelief. "I don't think I'm gonna do six. Two, maybe, but no more than three."

"Why not? Don't you want a bunch of little Castle babies running around?"

"Excuse me, but you're not the one who would have to squeeze out those six kids through a tiny hole in your body. And besides, I already have a giant Castle baby running around. Why would I want six more?" Kate didn't even bother trying to keep the teasing out of her voice.

"Ha ha, very funny," Castle responded in his normal volume level, momentarily forgetting the other presence in the room.

Luke stirred and began to make whimpering noises. His tiny eyes fluttered open and his whining got louder.

Kate shot her fiancé an annoyed look that read, "Way to go, dumbass," and then bent over to pick up the boy. She cradled him upright with her right arm coming under his bottom to support him, his face pressed into her chest. Her left hand was free to make soothing circles on the infant's back as she rocked slightly back and forth, cooing to him softly.

Castle looked on with a mixture of awe and wonder. He was so in love with this woman and he couldn't wait to start a family with her. If she was like this with a child she hardly knew, what would she be like with their own baby? Probably inseparable, he thought to himself.

Luke finally calmed down and the writer noticed his eyes close. All of his movements stopped as he fell back to sleep as Kate kept rocking him.

Glancing at the man staring at her with love and adoration in his eyes, she said, "Castle, I'm not gonna be able to put him down."

Picking up on her meaning, he replied, "You know that it's not recommended that infant's sleep in their parents' bed with them, right?"

Kate nodded. "I know, but it can't hurt to just try it for one night."

Castle took a couple steps closer to Kate so that the distance between them was almost none existent. He placed two fingers under her chin and lifted her face to his. The inches separating them disappeared as Castle's mouth found hers. It was chaste and fairly quick, but not rushed. They never rushed a kiss like this. One that conveyed how much they cared for one another and how much love was between them.

He pulled back so he wouldn't crush the boy Kate was still holding, put a hand on her back, and then led her out of the guest room, shutting the door behind him. They walked back to their bedroom slowly in order to not awaken the sleeping child as well as to savor the peace and calm of the moment.

Upon reaching their destination, Kate laid the baby in the middle of the bed, swiftly climbing in next to him on his right. Her partner, in every aspect of her life now, laid down on Luke's left so that the boy was sandwiched in between the two adults. He was laying on his back, undisturbed by the fact that he'd been removed from the comfort of Kate's chest.

The badass detective, who could make grown men weep like little girls in interrogation, and the mystery writer, who could describe the goriest, most gruesome death in detail, were now reduced to mush because of a little baby. Both were laying on their sides, facing each other, smiles fixed permanently on their faces. Kate rested her right hand lightly on Luke's stomach, needing to have contact with him. Castle, in turn, covered her hand with his, gazing into her eyes. The intimacy of it all surprisingly didn't scare Kate. It only served to make her want this even more.

As they drifted off to sleep, Castle and Kate kept thinking the same exact thing.

One day, he thought.

One day, she promised.

So what did you think? Feel free to review and let me know. Thank you!