It's a Sunday evening when he finally hands her a thin manuscript, slightly dog-eared at its corners with how many times he must have proof-read the whole thing.
"The, uh, chapter you asked for," he manages, like she's his publisher. Kate gives him a once-over, notes the set of his jaw, the way his index finger stutters, heartbeat-fast, against his thumb the way it always does when he's worried about something. He's— nervous. Is he nervous?
His hands shake a little when she takes the pages from him. Oh, Castle. He's always been strangely protective of his writing when it comes to her: she still ends up being the first to read new chapters, every time, but she knows how much he can agonise over every single word when there's this added aspect of her opinion. Even though she always loves every word. Even though he's still her favourite author, after all these years.
Not that she would ever tell him. (He definitely already knows.)
"Thank you, Rick," she murmurs, soft as she can. Kate steps into him and he responds instantly, folding himself around her as his arms come up to wrap around her back. "You didn't have to."
She feels the rough shake of his head against hers.
"I did. It's different this time," he responds, cryptically. She breaks away to frown at him, but he doesn't give much more away. "Just— read? I'll, um. I'll be in the bedroom."
With that, he pulls back, pacing off back to their room so fast that she can't even really think about following him. God. He hasn't killed Nikki off, has he? The anxiety cards from him in waves and she only watches, only takes a seat back down on the sofa and stares at the door for a few minutes after it shuts behind him.
Then she starts to read.
It's a good chapter. It's a great chapter. Kate's not even sure what he was really worried about — more than anything, she's excited to finish just so that she can find him in their room and tell him how much she loves it. He's been letting more and more of their life together slip into the relationship between Nikki and Rook, these days, and she loves it: the way her mannerisms have started to catch and entwine with Nikki's, the way Castle's descriptions of Rook's affection so ardently echo his own.
This chapter in particular: almost every new sentence is some study of Nikki and her beauty, her kindness, and Kate softens a little more with every description of how the light catches her "ethereal" features. Maybe it's a little much, maybe it doesn't matter. It's Castle's: it's perfect.
They're on a date. It's strange — Castle doesn't often take to describing this more intimate side of the Nikki-Rook relationship, and when he does the moments tend to be punctuated with scenes so explicit that she almost wants to call her dad and warn him. But there's no intonation of that, here, no undercurrent of Rook's lust, and Kate finds herself almost waiting for something bad to happen. Can a Nikki Heat chapter even be this peaceful? Is Castle about to reveal some time bomb which has been ticking away this whole time?
She reads on, unanswered. Minutes pass, and the tranquillity keeps up: they're in her apartment, he's cooked her a pasta dish, they're a couple of glasses in, and then—
Oh.
Her breath catches.
When Nikki looked up again, she blinked at the empty chair across from her. It only took a second, though, for her to register the next new thing: her partner, crouched beside the table.
Jameson Rook, with a ring in his hand, down on one knee.
Her jaw drops. For a minute, Kate forgets the fact of her own relationship with Castle, lets herself get a little lost in just being a fan of his books, of this proposal — she feels like a teenager, grinning away about some fictional couple, but it's just so perfect. She reads on, eyes skimming over the pages now, truthfully more eager to just go and tell Castle how much she loves the chapter than to actually finish it.
A proposal. Quiet, intimate, soft. Kate's heart sings at the thought.
She finally reaches the end, swallowing down an odd wave of emotion as she does. It's beautiful. Of course it's beautiful. It's his.
Kate stands, sets the manuscript down.
"Castle," she calls, heading towards their room, "Castle, it's gorgeous. You have no idea. People are gonna love it."
No reply, which is strange, but she's been reading for maybe twenty minutes now. There's every chance that he's fallen asleep.
"Rick," she tries, gentler, nudging their door open. "Still awake?"
He is. And he's… wearing a suit?
Castle's sat on the edge of their bed, peering up at her with shining eyes. An expression torn between reverence and fear.
Kate grins a little in response, tilts her head in question, starts towards him slowly.
"What did you think?"
His words are soft. Endlessly so. Almost inaudible in the quiet of this room that they share.
"It was beautiful," she returns, slowing to a stop before him. "Like I said. Seriously, Castle. Amazing." Kate blinks against the returned wash of sentiment which took her over before.
"Yeah?"
"Yeah." She presses her hands to either side of his jaw, holds his face between her palms. Have his eyes always been this blue?
"What was your favourite bit?"
"The, um. Proposal," she murmurs, faltering slightly. Very suddenly, all at once, a strange sense of understanding starts to set in. Is— this…? "Obviously."
"Okay," he whispers, his voice breaking a little over the words. "Okay, well. That's good."
Castle takes a breath, swallows. His hands are shaking again.
"Because, um."
Candles, Kate realises. He's lit candles, three of them, all flickering away on her bedside table. And he's in a suit.
Holy shit. Holy shit.
She's too stunned to really react as he pushes her gently backwards, leaving a gap between them which— is he—
He's moving. He's filling the space, shifting downwards off the bed, dropping to a knee on the hardwood even as Kate has to clamp a hand to her mouth to stop herself from sobbing out loud.
"Kate," he starts, peering up at her with an expression so full of love that it almost knocks her over. He's looking at her like she's the sun. "Katherine."
"Rick," she mimics, mostly just for something to say. "Richard."
He smiles gently.
"I think I've wanted to ask this question since about three seconds after you accused me of murder at my own book release party."
She laughs, but not really. Mostly it's just tears. Just joy.
"Do you remember that? God, your hair was so short. I loved it then." He pauses. "I love it now."
Oh, Rick. She loves him like breathing. A part of her always has. Does he know? Does he know?
"And I just— you know, I was writing that scene, and it was so perfect, and then I realised that the reason it was so perfect was because all I could think about was you."
Castle reaches forward, takes her hand. Kate can feel her heartbeat in her fingertips, and maybe he can too — the warmth of it all, joy suffusing through her veins like the sunrise. The expression on his face is like liquid gold, molten glass. He keeps going.
"Always you. It's always you, Kate." Then he pauses, lets the sentiment seep like molten glass into the atria of her thundering heart.
Devastatingly slow, he reaches into his pocket, tugs out this gorgeous velvet box which she can hardly even see through the haze of tears. It's a deep purple. Her favourite colour. Oh, he loves her so much.
"Then I finished writing, and I just knew. I couldn't go another day without doing this. I'm not sure I'd be physically capable."
He takes a shuddering breath.
"Katherine Houghton Beckett." He breathes her name like it's a prayer. Like it's all he knows. "You are… the strongest, kindest, most extraordinary woman that I have ever had the privilege of meeting. You're a dream that I'm still waiting to wake up from. You're the sun."
Castle opens the box. Draws out a ring. Lets it glint up at her, lit aureate by the soft light of their bedroom.
"I would follow you into the end of the world. Over and over."
Always. It goes unsaid. It's written into every line of his face.
"Will you marry me?"
Castle hardly even has time to ask the question to ask the question before Kate's barrelling into him, crashing down, losing sight of everything except the fact of her lips on his. She's breathless, banding a desperate arm around Castle's neck, her mouth an open wound.
"Yes," she gasps, the word desperate as it spills into him. He breaks away just to look at her for a second, the sheer joy in his gaze so all-consuming that she nearly forgets how to breathe. "Yes, Richard Edgar Alexander Rodgers Castle, I will marry you. I love you. I love you so much. Oh god, I love you so much."
And then he's kissing her again, and nothing else matters. Only him. Always him.