To Jess, the sparkliest mouse that ever lived. Thanks for existing. Happy belated!

"Harper. You cannot be serious. You're not serious, right?" Jillian half-demands, half-asks her little sister as she stands in the doorway, looking at the outfit she has chosen for her Friday night doing god-knows-what with god-knows-who.

In the mirror, Harper glares back at her sister. "What's it to you?"

"Seriously? How can you even ask me that?" Jillian clenches her fists at her side, wills herself to not barge into Harper's room and shake her.

"Oh, right. You need to call me out to keep up with the good girl routine. Well, go ahead, warn Mom before I try to get past them. May as well." Harper sighs dramatically, daring her sister to take the bait.

But the eighteen-year-old has wised up over the last few years. She knows better.

She just wishes she knew enough to get through to the utterly ridiculous rebellion her sister is going through. Putting them all through.

It's honestly exhausting.

"Harper Grace," she finally manages – and the full name does the trick, makes her unwillingly turn around. "Where are you going tonight?" Jillian asks when she is sure she has her attention.

Even though she knows the question is futile. Harper never tells. And, for reasons she doesn't quite understand, their parents have all but stopped asking.

Instead of one of her normal biting responses – none of your business or, simply, out – she shrugs. She suddenly looks small.

Jillian risks it and steps inside the room. Harper stiffens, but makes no move away from her.

"You don't know?" Jillian finally supplies after taking a few cautious steps into the room she never gets to see inside of anymore.

Harper shrugs again, averting her eyes.

"Okay," Jillian responds slowly, trying to piece it all together in her head, desperate to keep this line of communication open, pathetic as it may be. "Well. Who are you going with?"

Harper shifts from foot to foot, obviously nervous, still refusing to make eye contact.

Jillian starts trying to piece it together: not sure where she's going, but obviously knows that whoever she is going out with is trouble.

"You know. Friends."

"Plural?" Like, as in, not just some guy? She just barely manages to keep that question to herself. But by the look on her sister's face, it's obvious what she's asking.

"Uh. Yeah." Harper looks up then, flashes a sort of grimace-smile, then turns back to the mirror. "Running late though, so I have to finish getting ready," she supplies, abruptly ending their talk.

Jillian hesitates, but ultimately decides it's not worth it to start an argument by digging for more information.

"Okay. Well. I think we're ordering in, if that sounds at all interesting to you."

She decides to walk out before she has to see her sister's reaction to that semi-request. No matter how often it happens, her sister's blatant rejection cuts through her every time.

She tries to keep her frustration under control, tries to be understanding, tries not to let her little sister see how very aggravating she can be.

As she walks out and turns the corner to head downstairs, she almost runs right into her mom.

Her mom, who is right outside Harper's door, clearly eavesdropping.

Well, she has the decency to look embarrassed about it, at least.

She nods her head to indicate to Jillian to follow her downstairs and Jillian complies, unsure of what exactly her mother wants from her.

Kate is frozen outside her younger daughter's bedroom. She was about to stop in and ask Harper if she was going to be home for dinner – yeah, right – but stopped when she heard voices inside. And she knows she should have turned around and left as soon as she realized her daughters were actually speaking to each other in full sentences (well, close enough), but she found herself unable to walk away.

And, of course, talented and experienced detective that she is, she should have been able to sneak away before Jillian literally ran into her, but she was made so breathless by the conversation that she couldn't make the move in time.

Jillian, her bright, loving eighteen-year-old daughter, interrogating her, uh, less loving sixteen-year-old daughter.

Okay, less loving isn't a fair assessment. She hopes. Just less… vibrant? Or something.

But it was an actual interrogation. She could practically hear Jillian's thought process – after the nervous pauses of her sister, the puzzling out of pieces, the careful approach of her questions –

Geez, how much time has the girl spent at the precinct, anyway?

By the time Jillian is walking out and Kate realizes she is about to get caught, she decides she needs to have a talk with her anyway and may as well go ahead with it.

Downstairs, of course.

She walks over to the couch, knowing Jillian will follow, sit in her favorite corner, and pull the old quilt over her.

Once they're both situated, she takes a deep breath, and dives in.

"Jillian. You know you don't have to parent her, right?"

Jillian looks shocked by this announcement.

Okay, maybe it's worse than Kate thought. Have they dropped the ball so badly that they've made Jillian feel like she had to step in?

"I know," Jillian responds slowly, as if talking to someone who doesn't quite understand English. "I think it's called sistering?" Kate's eyebrows go up at that, and Jillian rushes to correct herself. "I mean, that's not a word. Obviously. You know, don't tell Dad I just said that. Why is parent also a verb and not sister? Because that's what I'm doing. Or trying to do. Sister her." Jillian must realize she's rambling and abruptly cuts herself off, her cheeks pink with embarrassment.

That's the Castle in her – stumbling over her words in a hurry to explain herself, especially when she thinks she's done something wrong.

"Jill, I'm not mad at you. You're not in trouble," Kate starts, wanting to reel her in before she works herself into any more of a Castle tizzy. "I just want to make sure you don't feel obligated to do something. You're a kid yourself." At the wince on Jillian's face, she corrects herself. "An old kid, yes. But I mean a kid as opposed to a parent. A daughter. You can leave the parenting to your dad and me. You know that, right?"

Jillian hesitates, and Kate suddenly feels like she was punched in the gut. Does her daughter think she's a bad parent?

She must get pale, because Jillian is rushing to fix it. Again.

"Oh no, Mom, it's not like that. I just know you guys are, uh, having a hard time with her, so I thought I'd see if I could talk to her. Get some intel, maybe? It's not like I think you're doing a bad job or anything like that. I just wanted to help. You and her. I didn't mean anything by it –"

"Jillian." Kate finally cuts in, desperate to make her daughter stop fumbling over some sort of apology for a wrong she didn't commit. "Again, not in trouble."

How can she possibly explain to her what she means? And how have they let Jillian feel like she needs to overcompensate so much?

She needs Rick for this. He is better at communicating with Jillian.

"You know what, honey? Let me just grab your dad."

Before Jillian can protest, Kate is off the couch.

She returns moments later with Castle in tow – it took only I'm having a Jillian problem for him to follow her right out into the living room – and he starts talking before they've even fully sat down.

"Hey, Jilly Bean, what's up?" Castle dives right in. She probably should've given him more information, but she was afraid Jill would leave or at the very least have time to reconsider her honesty –

Great. It appears as though she has decided this is an interrogation. No wonder that's how Jillian talks to her sister.

"Um. Nothing is really up, Dad," Jillian responds on a shrug, eyes averted. Castle looks over at Kate, his eyes a little wild.

Oh. Well, she told him she had a Jillian problem and now his daughter won't look at him, so he probably thinks something terrible has happened.

"I was about to go ask Harper if she would be home for dinner when I overheard Jillian speaking to her in Harper's bedroom. I may have, um, listened in to some of their conversation." Kate pauses, shifts guilty eyes to her daughter.

To her credit, Jillian doesn't bother calling her mother out on her word choice. Or her actions.

"I see," Castle responds slowly, obviously still trying to get a grasp on the situation. "Were our girls talking about anything special?"

"I just wanted to see if I could find out where she's going. Who she's going out with. Since you guys have been, you know, having some trouble with her. I thought maybe she'd talk to me a little. Or, like, have dinner with us. I didn't mean to make more trouble, I was just – "

Instead of verbally cutting her off like Kate wants to do, Castle slides over to her and puts his hand on her knee, a comforting gesture that stops the rambling immediately.

Kate tries not to beat herself up over the fact that she doesn't know how to reach Jillian as well. Or, apparently, Harper. Crap.

"Kate." Castle's voice, low and warm, brings her back into the moment. It must've been all over her face.

She takes a deep breath and brings out a smile for them, for her husband and her daughter who are both so full of life and light and joy that they sometimes can't even stem the tide of their words, that the thoughts and pictures and love just pour out of their mouths like it's unstoppable.

"Jilly," Castle finally speaks up again after a long moment, "you know you're not responsible for her, right? We're her parents."

"I know, Dad, and I'm so sorry – "

"Let me finish." Castle uses his stern voice to cut her off, squeezing her leg where his hand still lies.

Jillian nods once, and Castle goes on. "But you can talk to your sister anyway you choose. As long as it's with respect, of course. She may be quieter than you and may be harder to reach, but she's your baby sister, and we aren't here to tell you not to talk to her. We'd never do that to you, or to her."

Jillian nods again, all that tension leaving her body as her father seals his words with a tight hug.

"You're a good sister, Jilly Bean. And Harper loves you. Even if that's not obvious all the time," Kate chimes in, suddenly feeling a little too left out of this interaction, of this thing she started with her motherly nosiness.

Castle nods in agreement with her as he lets Jill out of his embrace. "Okay, so that's that. Now, who wants Chinese?" And then he is up and in motion again, rendering his question moot as he picks up the phone.

But Kate and Jill smile up and him and agree, and he walks towards the kitchen to place their order.

"I'm sorry," Kate says softly after a moment of too much stillness, too much stiffness re-entering Jillian's demeanor. "I didn't mean to invade your privacy. You have a right to a private relationship with your sister. I just wanted to make sure you don't feel stuck. Your dad and I never had siblings, and sometimes we aren't sure what it's supposed to look like or whether we're doing it all wrong. But you seem to have a better handle on it than we do. You're not doing it wrong. Okay?"

Jillian nods and then suddenly Kate is caught up in a hug. Reflexively, she wraps her arms around her older daughter – eighteen already and almost ready to go to college, Kate can hardly believe it – and whispers her love in her ear.

They sit on the couch to eat, forgoing the formality of the table for a relaxed late night takeout binge. Halfway through, Kate hears the so soft footsteps of her youngest daughter coming down the steps. Before she turns her head to look, she steels herself, trying to prepare for whatever outfit her daughter has deemed appropriate for the evening.

When she finally turns out, however, what she sees is a girl who looks more kid than teen, wearing a pair of flannel pants and a t-shirt, her long hair tied back in a loose braid, her face free of makeup.

Neither Castle nor Jillian has noticed; Kate's always been more in tune with Harper's quietness. She walks over to the stairs, avoiding alerting them, standing at the bottom and looking up at her daughter, who froze when she made eye contact with her mother, as though unsure what her next move is supposed to look like.

"Hey, HG," Kate starts, using the nickname she hasn't brought out in a while. "We still have a ton of food left. You know how much your dad orders. Wanna come eat?"

She feels a certain amount of sadness over the fact that she needs to expressly invite her child to eat dinner with them, but she doesn't let herself dwell on it. Instead, she focuses her energy on looking as warm and welcoming as possible.

After a long minute, Harper nods and finishes walking down the stairs.

Kate suppresses the urge to pull her into an embrace, and instead opts for a soft kiss on her head and a brief brush of her hand on her back – enough contact for Harper to relax, but not so much to stifle.

So much like her mother, or at least how her mother used to be. And she knows that if Harper just spent more time with them, with her father, he could pull out the light like he did all those years ago for her.

For now, Harper's silent agreement to spend this one random night at home will have to be enough.

They walk over to the couch together, and she silently thanks the universe that neither Castle nor Jillian make a big deal out of her arrival.

Instead, they smile at her, hand her a plate, and continue their heated argument over which science fiction series is the most well-written.

Harper and Kate share a secret eye roll at their enthusiasm.

And, in that moment, Kate is sure that whatever tomorrow brings, whatever the next five years bring, Harper will come out the other side. And their family will be stronger for it.