Entirely speculation, most likely will not happen. Huge spoilers for the finale.
She never feels alone. Not once. She can remember last year, remember with blinding clarity how dealing with her mother's case left her alone, just barely keeping her head above water, no one to act as dry land. She can remember, and God isn't that what screwed everything up in the first place?
Only, it doesn't feel so screwed up any more. Not when he sits next to her in the precinct corridor, his thigh so close to hers that she knows he can feel her trembling. He passes her a cup of coffee and she takes it, her lifeline, their strongest tie.
He meets her eyes, every line of his face serious. "You're not in this alone."
She can't look at him, focuses on his hand where it rests against his knee. "I know," she says, and then she takes his hand in hers. It's the same hold as that awful day in the bank, as the day she came to his loft and listened to his mother's life story and went into the woods with him. His fingers are so warm in hers that she startles for a second, but then she relaxes into it and his fingers tighten just a little. Not enough that she chokes, just enough that her heart's rhythm quickens imperceptibly.
They sit like that until Ryan comes to find her with a new lead and very pointedly does not look at their still joined hands.
She's doing okay, she really is. Well, of course she sobbed herself into a stupor when she got home – ridiculously late – from the precinct yesterday, and then spent the whole night on the couch. She kept finally falling asleep and then being wrenched from it by vicious nightmares in which he is quick enough and he takes the bullet, over and over and over.
She's doing okay, and then he intercepts her as she's coming out of the bathroom at the end of the day and he asks her if he can show her something. Her heart soars in her chest and she thinks, she really does, that this is it. That he's going to show her his heart.
Only he doesn't. He shows her his murder board. Tells her that some guy phoned him after she was shot, telling Rick that if he could keep her away from the case, the guy would keep her safe.
It burns through her, searing her veins, leaving a trail of molten agony. She can't see straight, her blood rushing into her ears and her eyes and she can taste it at the back of her throat, feel the heat of her pulse jumping in her neck.
She stalks towards him, her teeth gritted, her voice low and predatory. "How could you cut a deal for my life?"
He tilts his head to the side, doesn't hesitate. "Because I love you."
She doesn't allow herself to react, doesn't stop to wonder over the nonchalance with which he says it. It's the second time he ever has; only the second time, but he seems tired. Maybe it's because the words drag up the pain of the past month, the secrets between them now both bathed in light and all the uglier for it.
She can't allow the heat of an entirely different kind to surge through her, heal the pain. She's just so God damn pissed. "How the hell could you do this?" she hisses it at him. He doesn't flinch.
Just steps towards her and grips her upper arms. "I hear the words 'keep you safe' and I'll agree to it, whatever it is. Even if it means you hate me, even if I lose you, I don't have a choice. I can't watch you die again."
She shrugs him off and tries to ignore the gaping hole that opens in her stomach as he turns away slightly, closes his eyes. "What about me, huh? You think I can watch something happen to you. What if they come after you instead of me, what if you get too close? You've got no back up, no gun. You're a civilian. Yes, you're my partner, but you're not a cop, Castle."
He opens his eyes then, and they're gleaming, alive with the fight she's so missed in him. "I'm more than a partner."
She closes her eyes now, realises with an abstract sense of wonder that it helps not to have to watch. "This is not your fight, Rick. You shouldn't have to risk your life for me."
She's retreated to the corner of his office almost without knowing, paces there like a caged animal.
"It shouldn't be yours either. You have to live your life." She can hear his heart breaking in every word that crosses the barrier of his lips.
She shakes her head, hair flying around her face. "I told you, I have to put it to rest."
Yes, she told him that. Eight months ago. Just last week she told him she's almost ready. She can see that she's getting sucked down the rabbit hole again, but she's watching behind the glass, unable to cry out, to stop herself.
His head bows. "Please"
She can't. "Castle."
She's about to walk away, about to go back to her apartment and stare at her own makeshift murder board some more when he plays his final card, his last hope.
"I love you Kate, if that means anything. Just don't do this."
She didn't want to look at him but she does anyway, can't help but stare at the tears swimming in his eyes.
She shakes her head. "I'm sorry, Rick. I have to."
She walks away.
She's in the kitchen when she hears the noise, freezes. She can't move, it takes everything she has just to turn around. Her heart is pounding against her ribcage, the bullet wound like a knife in her side. And then the adrenaline kicks in and she's creeping up the stairs, walking out onto her rooftop garden.
Stupid, Kate.
There's nowhere to hide up here, nowhere to run either. She sprints across the roof, can hear footsteps now. It all happens too fast then. She tries to fight, she does, but the guy is physically stronger than her and she just can't do it.
And then somehow she's falling off the roof, just managing to grab on to the ledge. She can't hold on, she can't.
His name falls from her lips, a plea and an apology both, and then she has to let go.
Somehow, she manages to fall onto the fire escape. It hurts. God, it hurts. Leaves her flat on her back, no air to even think with. She opens her eyes slowly, prays her assassin won't come to check she's dead, but she thinks he's gone.
She sits up slowly, every slide of bone against flesh agonising. And then the heavens open and it pours.
She knows what she has to do now. She runs. In the downpour, wincing with every step, trying to ignore her bruised and tender back, she runs to him.
He answers the door and she doesn't give herself an opportunity to back out, tries not to think about how horrific she must look with her wet hair hanging lank over her cheeks, wispy hairs sticking to her forehead. As he steps back to let her in she steps forwards and reaches out for him, cups his face in her hands.
He kicks the door shut and pushes her back against it, cushioning her back with his hands like he knows.
He presses his forehead against hers, his lips so close she can already taste them. "Are you sure?"
She smiles, and then she leans forwards and presses her mouth to his, kisses him with everything she has.
He sighs against her mouth, pulls back a little. "I'm so sorry."
She delves into him again, can't do sorry yet. Doesn't want to think, just feel. "Shh, later."
He laughs and she marvels at the way his throat works, has to dart out her tongue to see if she can taste his laughter from the outside. He shudders and cups her cheek. "What's happening now?"
She looks up at him from under her eyelashes. "Now? I'm freezing, I could really use a shower." She stretches up on her tiptoes to kiss him again, pressing the soft curve of her breasts against his chest. "Are you coming?"
He laughs again, his eyes crinkling at the edges. "Of course."