Kate was quiet as they walked down the hallway toward the apartment's front door. Rick had been trying to make conversation from the moment they entered the building, but Kate's only responses had been a nod or a quiet "mmhmm," and she seemed to be avoiding looking at him. He was having trouble reading her emotions—she didn't seem upset or angry, like she had been yesterday, but there was definitely something going on. She was probably just nervous about the job, and his attempts at humor clearly weren't working.

This was strange. Castle could always make girls laugh and smile, but not Kate. He'd only ever gotten a few shy smiles and one small giggle from her, but her laugh had made his heart skip a beat, and every smile had made his heart melt. No one had ever had that effect on him before. The reason her smiles were rare was probably because of all that had happened in her life so far this year. He knew there was little that he could do to stave away her sadness, but if he could make her smile, even just for a moment, his efforts would be worth it.

For the moment, though, if Kate really was nervous, he had no doubt that Alexis would quickly put her at ease.

"Well, here we are," he announced cheerfully as they arrived at his front door. He opened it, ushering Kate in as he called for Alexis. The child was in an adjacent room, and he heard her running to the door, chattering the whole way.

"Hey, Dad! That took so long! Did you find her? Was that her out- oh…" she trailed off as she rounded the corner, stopping when she saw Kate.

Castle chuckled. Alexis was usually shy with strangers. He had talked about Kate with Alexis numerous times this morning, hoping to ward off the shyness, but it hadn't worked. Alexis quickly crept over to him and wrapped her arms around his left leg, peering at Kate from behind her father.

"Alexis, this is Kate," Castle said. "Why don't you say hi, sweetheart?"

Alexis buried her face in her father's leg as an answer. Castle placed his palm on Alexis' shoulder and looked at Kate helplessly, shrugging. Kate, however, wasn't paying any attention to him. She was kneeling down in front of Rick, peeking around his leg at Alexis.

"Hi, Alexis," she said gently. "I'm Kate. It's very nice to meet you."

Alexis peeked out shyly from behind her father's leg, and Castle took the opportunity to gently nudge her forward. "Hi. I'm Alexis Harper Castle," she said quietly, holding out her right hand.

Kate smiled warmly. "That's a pretty name," she said encouragingly, shaking Alexis' hand. "And you have such beautiful red hair!"

"Thank you," Alexis said with a shy grin, pulling her hand out of Kate's and stepping out from behind her father's leg. "Do you wanna see my room?" she asked hesitantly. Kate agreed, and Alexis took her hand.

"Only five minutes until lunch, Alexis," Castle called as the two girls disappeared up the stairs. He shook his head as he walked toward the kitchen. Kate really was a natural with kids. She'd managed to break through Alexis' shell in mere seconds, and how she'd known that Alexis was insecure about her hair color was beyond him. He couldn't remember the last time his daughter had opened up to a stranger that quickly. Looks like I picked a good sitter, he thought to himself as he began setting the table for lunch. Kate wasn't just going to be good for Alexis, though. She was already beginning to have a positive impact on him as well.

The girls made their way back downstairs after a couple of minutes, and the sandwiches and apples were served. Alexis chatted enthusiastically with Kate all throughout lunch. Castle chimed in occasionally, but mostly stayed silent. He'd never seen Kate this animated before, and much as he wanted to talk, he was enjoying just listening to the two girls chat with each other. Kate obviously adored his daughter. Castle finally joined in the conversation, telling silly stories and jokes that were rewarded with peals of giggles from Alexis and plenty of unsuccessful "I'm trying my hardest not to laugh" faces from Kate.

After the meal was over, Kate insisted on helping Rick wash the dishes. "Really, Castle," she said admonishingly, after he'd refused her assistance twice. "You gave me a free lunch, and the least I can do to thank you is to clean up." He gave in, chuckling quietly to himself. You're getting soft, Rick, he thought, letting a nineteen-year-old-girl boss you around.

After all of the dishes were clean and put away, Castle turned around and was surprised to find Alexis sitting quietly at the kitchen table, a pout on her face.

"What's the matter, pumpkin?" he asked, walking over to his daughter.

"You promised, Dad… you promised we'd play laser tag before you left," Alexis said sadly. "And we can't play with three people."

"Yes we can, Alexis!" Castle said reassuringly. "I have two grown-up vests. Remember? I bought two so that when you outgrow the kids' vest, you can still play." Alexis lit up. "You'll just have to ask Kate if she wants to play with us," Castle continued, looking over at Kate. She was standing a few feet away, a half grin on her face.

Alexis immediately jumped up and hurried to Kate's side. "Kate," she said sweetly. "Will you pretty please play laser tag with me and Dad? It's really fun."

Kate looked at Rick, and he lowered his chin, giving her his best pleading, hopeful face. She giggled. "Of course," she answered, returning her gaze back to Alexis.

"Oh boy!" Alexis shouted excitedly. "You can be on my team! We're gonna beat Dad. I'll go get the gear," she added as she ran out of the kitchen.

Kate turned to face Castle. "She's adorable," she said with a grin.

Rick smiled proudly. "I think so, too," he nodded. "But I'll have you know, Miss Beckett, that having sheer adorableness on your team isn't enough to give you a tactical advantage. I have never lost a game of laser tag." He puffed his chest out with pride, but quickly deflated when he saw the look that Kate was giving him. "Okay, okay, so I've let her win a few times. But I've never lost on purpose, and that's what's the most important."

"Well, Mr. Castle, there's a first time for everything," Kate said, taking a step closer to him.

Castle raised his eyebrows. "Is that a challenge, Miss Beckett?"

"It certainly is, Mr. Castle," Kate replied seriously.

Castle was amused. "In that case, let's have a little wager," he said playfully. "If you win, I'll bake you a batch of your favorite kind of cookie. But if I win, you have to have lunch with me tomorrow afternoon."

Kate took another step toward Castle and stood on her tiptoes, her nose almost touching his. "Deal," she said, eyebrows raised.

After a two-hour battle, the game was called. Kate and Alexis had lost spectacularly. Kate would never admit to Castle that she'd secretly promised the child extra ice cream that evening if they let her daddy win. Lunch with Richard Castle seemed like a pretty sweet deal in exchange for losing a game of laser tag.

"Alright, Alexis. You're the expert here. Tell Kate what you do every night." Castle said. It was 4:55, and he was about to leave for his mother's play. The temptation to skip the play and stay home with Kate and Alexis was overwhelming, but wouldn't have been able to rationalize that decision with his mother.

Alexis proudly took charge. "Well, I go to bed at 9:00 every night," she started. "I always brush my teeth and wash my face before bed. Then I have to have a bedtime story. Dad usually tells me about the adventures of Prinja, but he makes it up, so I guess you can just read me a book."

Kate looked at Castle, a confused expression on her face. "Prinja?" she asked.

"The princess ninja, of course," he answered matter-of-factly.

Kate smirked. "How cheesy," she muttered.

Alexis, ignoring their exchange, continued. "I clean up my room before bed, too. You can help me with that. And that's it!"

Kate looked toward Castle, and he nodded in agreement. "Good job, sweetheart," he said, patting Alexis on the back. The child smiled proudly.

"You're going to make sure all of the windows are closed and the front door is locked, right?" Castle asked his daughter. "And you're going to make sure Kate knows that the emergency phone numbers are posted on the fridge, and that she turns off the stove after she cooks the macaroni and cheese?"

"Don't worry, Dad," Alexis chided. "We're going to be fine."

Rick chuckled. His daughter was six, going on thirty. He had no idea where her strong sense of responsibility had come from.

"Okay, good," he said, bending down to give Alexis a kiss. "I'll be here when you wake up in the morning." Castle straightened, then turned to look at Kate. "My cell phone number is on the fridge. Don't hesitate to call me if something goes wrong."

"Don't worry, Castle," Kate said with a smirk, echoing Alexis' words. "We're going to be fine."

He laughed. "You girls have a good evening," he said, picking up his coat. Castle walked out the front door, feeling confident that he was leaving his daughter in good hands.

It was silly, but Kate was sad that Castle was leaving. It had been a whirlwind of an afternoon, and she didn't realize how much Castle had contributed to the fun until it was time for him to go. When he finally shut the front door, Kate stepped toward it and turned the lock, then returned to Alexis' side.

"So now that your daddy's gone, what do you want to do?" Kate asked, kneeling down to match the child's height.

Alexis cocked her head to the side for a moment, thinking, then put her hands on her hips and looked at Kate intently, almost as if she were interrogating her. "Are you good at playing Barbies?" she asked sternly.

"I'm the best Barbie-player you'll ever meet," Kate replied as seriously as she could, matching Alexis' solemn tone.

Alexis relaxed, smiling. "Good! 'Cause Dad is really bad at Barbies. He never does it right." She took Kate's hand. "Come on," she said enthusiastically, leading Kate to her bedroom.

As they were removing Alexis' Barbie collection from her closet, the child explained the Barbie game. "There's a mommy and a daddy," she said authoritatively, "and they have two girls. And they have a bunch of friends. They like to go on picnics sometimes and play in the park. Dad always tries to make them be spies or ninjas or other silly stuff," she added.

Kate giggled. She could definitely see Rick doing that. "Well, he's just wrong, isn't he?" she asked.

"Yep," Alexis nodded, continuing to remove Barbies from their boxes. "The big sister likes to take care of her little sister, but the big sister likes to skip school and stuff, 'cause she's a teenager, and that's what teenagers do, I think," she continued. "And the little sister loves her big sister a lot. And they both love their mommy and their daddy, and the mommy and daddy love each other very much."

Alexis stopped unloading Barbies and looked at Kate. For the first time, she looked insecure.

"I wish I had a big sister… and my mommy never comes to see me," she said quietly, lowering her chin.

Kate's heart broke as she realized that Alexis acted out her ideal family every time she played with her Barbies. She knelt down in front of Alexis and gently placed her hand on the girl's shoulder.

"You know what, Alexis? I have an idea," Kate said gently. "How about I be your pretend big sister?"

Alexis' eyes widened as she raised her head. "Really?" she asked hesitantly.

Kate smiled. "Really. I can be your pretend big sister every time we're together. How does that sound?"

Rather than answer verbally, Alexis stepped toward Kate and wrapped her arms around Kate's shoulders. "I've always wanted a big sister," she whispered, pressing her cheek against Kate's chest.

Tears sprung to Kate's eyes. This child was the sweetest, most precious little girl she'd ever known. Pretending to be her big sister would be easy.

Pretending to be her Barbie big sister, however, proved not to be so easy. Alexis knew exactly how she wanted the Barbie big sister to act, and when Kate had her do something "out of character," she was scolded ("Come on, Kate, you're not doing it right!"). Eventually, the Barbies were put back in their boxes, and their gourmet dinner of macaroni and cheese was served, with ice cream for dessert. Alexis had reminded Kate about her promise of extra ice cream no fewer than seven times. Castle could never forget anything, the way this child is, Kate thought with a grin.

Castle had mentioned to Kate that Alexis was the portrait of responsibility and would probably take charge of her own bedtime. Sure enough, Alexis interrupted their movie that evening with a panicked announcement.

"Kate, the little hand is on the eight, and the big hand is on the six. Do you know what time that is?"

Kate decided to feign ignorance. "No, Alexis, I don't. What time is it?"

Alexis jumped off of the couch. "It's 8:30! That means I go to bed in thirty minutes! We have to stop the movie! I have so much to do," she continued, chattering aimlessly as she hurried up the stairs.

Kate turned off the movie, giggling, and followed Alexis up the stairs. From what she'd seen of Castle, it was apparent that Alexis' sense of rigid responsibility had not been inherited from him.

After the child had brushed her teeth, washed her face, and changed into her pajamas, she picked a book, and the two girls snuggled into Alexis' bed. Alexis wanted to show off her reading skills and insisted on reading the majority of the book aloud, sorrowfully asking for help when she came to a word she didn't know.

"Thanks for reading with me," she chimed as Kate put away the finished book. "But now, you have to check for monsters. They like to hide under my bed, so Dad always checks to make sure they're not there."

Kate crept silently back toward the bed, a finger on her lips. Alexis nodded, hugging her knees to her chin. Kate slowly ducked down to her knees, gently placed her fingers around the edge of the bedskirt, then quickly yanked it up. Alexis looked at her, a serious expression on her face. "Are there any monsters?" she asked hesitantly.

"Not a single one," Kate answered reassuringly, straightening. "If there were, I would have snuck up on them and scared them!"

Alexis smiled and laid down, snuggling deep under the covers. "Goodnight, Kate," she said sweetly. "Will you still be here when I wake up in the morning?"

"No, baby," Kate replied sorrowfully, stroking Alexis' hair. "I have to go home." Where she'd go, she didn't know. But there was no way she'd spend the night at Castle's place. Lunch and dinner were one thing, but sleeping over was another thing entirely. Not to mention that it was him, and this was his house. Much as she idolized Richard Castle, she wasn't going to be that fan.

Kate stepped into the living room and sat on the plush sofa. Alexis was in bed, and Castle said he'd be back around eleven, so she had a couple of hours to herself. She turned on the TV and began flicking aimlessly through channels, finally stopping when she found something she recognized. "Nebula 9" reruns were on. Kate grinned, settling back to watch her favorite show. The show had been cancelled at the end of its first season, and its last episode aired the week before her trip to Vegas. Much as she hated to admit it, she'd cried when the cancellation announcement had been made.

She'd barely finished the end of her first episode when she heard Alexis calling her name, frantically. Kate jumped off the couch and raced up the stairs, hurrying to Alexis' side. The child was sitting up in her bed, a look of terror on her tear-streaked face. Kate sat down on the bed with Alexis, wrapping her arms around her trembling body.

"There was a m-m-monster," Alexis sobbed. "It c-came out from under my b-b-bed. It s-scared me."

Kate rubbed Alexis' back, soothing her. "Shh, it was just a dream," she whispered. "There weren't any monsters under your bed earlier. Remember? I made sure. It was just a dream."

Alexis sniffed. "It s-snuck in after you left," she said, wiping her eyes.

"Well, that won't do," Kate said. "No sneaking monsters allowed in this house!" Alexis grinned, sniffling.

"I have an idea," Kate continued. "Since I'm your big sister, how about I stay in here with you for a while? Those monsters won't bother you if I'm in here with you."

Alexis nodded and laid down, her face turned away from Kate. Kate pulled the covers over Alexis and laid down beside her, gently stroking the child's silky hair. Her mother used to do this to Kate when she'd had nightmares as a kid, and it had never failed to soothe her. She closed her eyes, continuing to stroke Alexis' hair long after the child had fallen asleep. Even if she wasn't really Alexis' big sister, it was nice to feel some semblance of family again.

It was 12:45 AM, and Rick was finally getting home. His mother had convinced him to go to the afterparty with her under the guise of "The real star of the show doesn't go to the after party alone, darling. Besides, it wouldn't hurt you to be seen either." Judging by her actions, though, the real reason Martha had wanted him to attend was to introduce him to the show's lead actress ("I'm telling you, darling, she's the most talented girl you'll ever meet. And she's single!"). He'd finally managed to get away, knowing he needed to get back to Kate and Alexis. Rick would make sure and apologize to Kate for his late return. He didn't want her to refuse to babysit for him again for fear of his lateness being a regular occurrence.

Rick unlocked the front door, opening it quietly so as not to wake Alexis, and stepped into his apartment. The TV was quietly playing when he walked into the living room, but there was no sign of Kate. After searching the kitchen, study, and master bedroom, he still hadn't found her. Surely she didn't leave, Castle thought, panicked. He'd check on Alexis, then continue his search for Kate.

He quietly opened the door to his daughter's bedroom and peeked in. What he saw made his heart catch in his throat.

Kate and Alexis were both in the child's twin bed, asleep. Kate had her arms wrapped protectively around Alexis, who was snuggled in, breathing slowly.

Rick stood in the doorway, smiling as he watched them. A casual observer would have never guessed that the two had only met that afternoon, judging by the way they were cuddled together. He finally stepped in quietly, praying the girls wouldn't wake, and tiptoed over to Alexis. He gently kissed her cheek. "Goodnight, princess," he whispered.

He took his eyes off of his daughter and looked over at Kate. She looked so peaceful and vulnerable in her sleep. Rick reached out and gently brushed a loose strand of hair out of Kate's face, praying she wouldn't stir.

"Sweet dreams, my sweet Kate," he said softly.

He walked back to the doorway of the room and turned around once more, letting his gaze linger on the sleeping girls for a while longer. He had a feeling that Kate hadn't fallen asleep with Alexis intentionally. Alexis had probably just had a nightmare (they'd been much more frequent lately), and Kate must have fallen asleep comforting her. The thought made him smile.

Kate fit easily into his family.

Author's note: In writing this chapter, I learned what writer's block is. And I learned that it's not very fun. I struggled for so long to get any words down. The help of my lovely beta/personal story assistant/totally awesome person Cathey is what finally helped me to get this chapter published, and I cannot thank her enough. She's a magician. Seriously.

As always, reviews are appreciated. I read each one of them.