As soon as he meets Kate Beckett, Richard Castle starts writing a story in his head.

(A story that will end up being theirs).

It's the story of a tough-as-nails cop and the mischievous writer who follows her around; the story of Nikki Heat and Rook.

Castle loves it too much.

()()()()()()

The first time he saves her, they're standing in an apartment holding a knockoff purse and smuggled passports in their hands.

Castle glances around the kitchen, and suddenly there's a large, scary man pointing a gun in their direction, and Castle just reacts. He pushes Beckett to the ground just as the bullets start whizzing over their heads, and this is somuch scarier than he thought it would be.

They crawl behind the large island that dominates most of the kitchen space and try to catch their breath. He's not going to get shot, he's not going to get shot...Beckett will make sure he doesn't get shot, right? Castle glances over at her, squinting through the shower of glass that rains down upon their heads.

Right.

They're partners, and no matter what she really says, she won't let him die.

His gaze snags on a small refrigerator full of champagne bottles. What would Rook do?Castle smiles as the question rings through his head. He has an idea.

()()()()()()

It works.

Obviously.

()()()()()()

"I'd say this deserves a toast." Castle's standing there watching Beckett handcuff the guy, and he feels something in his chest unfurl. He could have died, but he didn't, and the thought makes him light. His hands are still shaking from the adrenaline, so he almost misses his mouth when he takes a swig from the champagne bottle. He holds it out to Beckett, and to his surprise she stands up and takes it from him.

"Not bad, Castle," she murmurs, taking a quick sip before handing the bottle back to him.

"Was that almost a compliment, Detective?" he asks, and she rolls her eyes, walking out into the hallway to call for a paramedic. "It was!" he declares with a smile, bringing the champagne to his lips again.

()()()()()()

He can taste her on his tongue later as he whispers never, ever call me 'kitten'in her ear, and he realizes he could easily become addicted to her.

()()()()()()

Castle goes home that night and tries to put the whole thing in his book, because there's something so poetic and right about Rook saving Nikki Heat's life. He wants to capture that feeling in print so it's preserved for generations, so that years from now someone, somewhere, will be thinking about a detective and her writer.

(He wonders idly if it will be seen as a love story.)

He stops in the middle of writing the scene.

Beckett's not ready for something like this.

()()()()()()

He shakes her hand goodbye.

They've chased killers together, traded jokes over dead bodies, and tangled themselves up in each other's lives, and he simply shakesher hand.

He hates himself almost as soon as he does it.

"You take care of yourself," he says, and then he scrambles for something to say that will make up for the lack of feeling in his handshake. His phone rings.

Of course.

Then her phone rings.

Really?

"You know, you better get that," she says when they just stare at each other and let their phones ring.

He wants their goodbye to be so much more than this.

"Yeah," he finally says, and puts his phone to his ear. It's Paula talking a mile a minute about Heat Wavesales. Castle suppresses the urge to roll his eyes and focuses instead on Beckett and her conversation.

Paula regains his attention as soon as she says the words three more Nikki Heats. Castle's stomach flip flops, and he glances over at Beckett. He could probably write ten more Nikki Heats and still never tire of following her around.

"He wants me to what?" Beckett's voice cuts through Paula's blabbering, and somehow Castle can tell that her conversation now involves him.

"'Three books? That would take forever."

Castle can't help but think that foreveris exactly what he wants.

"-what makes things easier is that I already spoke to the mayor-"

He barely catches the last part of Paula's sentence, and he feels his throat quickly go dry. Beckett's going to kill him. "You already spoke to the mayor?" he asks, just to be sure.

Beckett spins around. "I'm gonna kill you," she hisses, and Castle realizes that they both are having basically the same conversation, just from different sides.

"No! No, sir, I was not talking to you," Beckett corrects as she grips her phone closer to her ear and glares at Castle. He bites down on a laugh, swallowing it, because if he laughs now he has no doubt that she will physically assault him and he'll probably end up dead.

"I think..." he trails off as Beckett hangs up and stalks over to him. "I'm gonna...Paula? I'm gonna call you back."

Maybe he should start running now.

Beckett's phone rings again.

"What?" The word is short and clipped. She is sogoing to kill him. Beckett pauses, listening to the person on the other end. "All right," she says with a nod, and then walks off.

"Where are you going?" Castle's not sure he can wait for her to kill him; the suspense will really be too much for him to handle.

"That was Esposito. There's been a murder."

For some reason this news is comforting.

Beckett turns around and faces him. "Are you coming or what?"

Castle smiles. "Coming." He jogs to catch up with her, and falls into place next to her with a grin. "Always," he adds as they step out onto the sidewalk and walk toward Beckett's car.

The sun beats down on them, glinting off the hood of the car. Castle squints up into the sky. "So, what do you think awaits us? Decapitated body? Body that appears to have been eaten by sharks? Ooh, how about the body of a former Soviet agent turned CIA operative?"

Beckett stops, stares at him over the top of her car, and rolls her eyes.

Castle keeps talking. "Let's make a bet! I win and one of the next Nikki Heat books gets some racy title like Street Heat, or Heat of the Moment, or oh! How about Naked Heat?"

Beckett cuts in, looking very unamused. "And if I win you never get to use the words 'CIA', 'mafia', or 'aliens' ever again." She slides into her seat and slams the car door shut.

Castle looks around at the faces of bewildered pedestrians nearby, and then laughs.

He never wants this to end.