Spoilers for the Squab and the Quail and Still READ NO FURTHER. BECAUSE WHAT THE HELL KATHERINE BECKETT!? Because this is how it's going to HAPPEN OKAY KATHERINE BECKETT YOU ARE NOT AN IDIOT. Um yes, anyway, this is my take on that promo.

He's not surprised when she lets herself into the loft, even though he'd told her that he wanted the evening for writing and he wasn't going to be distracted, not by a bottle of wine and the allure of the fire and her, not by anything. So when she comes into his office, and throws herself onto one of his overstuffed armchairs he gives her nary a glance. Or that might be because he's too immersed in whatever trouble he's got Nikki and Rook in this time. Or he's pissed at her. Probably all three. He has every right to be though. He'd warned her. He'd said. Vaughn is charismatic and charming and good looking and all the things every man aspires to be, but he is, essentially, a dick. She'd put it down to simple jealousy, which she could understand. She could. It wasn't like she stopped Vaughn's advances, it wasn't like she ever gave him the idea that he didn't have a cat in hells chance of what? Kissing her? A dinner date? A dinner date followed by kissing followed by a distinct lack of sleep and a walk of shame in the morning? No, she didn't exactly stop him in his tracks.

"I thought you were supposed to be on protection duty." Castle finally says, though he doesn't look up from his laptop.

"I got Esposito to cover." She replies, tipping her head back and staring at the ceiling.

"Why? Thought you got on well with Mr. Vaughn?"

"He tried to kiss me." Kate doesn't know what she expects him to do. Threaten to and kill him. Storm around and rant and rave about men. Drag her off to the bedroom and not let her leave until she knows that she's his and only his, and that no one can touch her ever. She doesn't expect him to just go oh and then carry on typing like it's no big deal. "I didn't kiss him back." Still nothing. "I did hit him though." That earns her a faint smile. "You were right."

"Was I? Oh, wow. That's a first. Kate Beckett actually admits she was wrong and I was right. Imagine that. It's a miracle."

"Castle… I'm trying to-"

"Trying to what? Apologise? It's not like you asked for him to kiss you. He's a good looking man, you're a good looking woman, I could hardly blame him for trying."

"That's all you have to say on the matter? I almost kissed a man who wasn't you, and all you can say is that you don't blame him?"

"You weren't exactly telling him not to. You flirt with a guy, he tends to think he has a chance. You were flirting with him, he took his chance. Therefore, he's not to blame."

"Fine, blame me."

Castle closes the laptop lid with a lot less anger than he probably feels and stands up. "Okay, it's your fault." And then he's gone, walking into his bedroom and closing the door behind him.

Kate sits there for a moment before hauling herself up and following him, switching off the lights as she goes. Castle's not there when she comes in, but she can hear noise in the bathroom. She pulls off her clothes, leaves them draped across the chair, rifles through Castle's wardrobe for that white shirt that she has a certain attachment to. "It's in the laundry." Castle is saying, coming out of the bathroom in his t-shirt and cotton trousers. "Pick another one."

She pulls the maroon shirt off its hanger instead, and shrugs it on, buttoning it up as she heads over to the bed. "I wouldn't have – I'd never have cheated on you."

"And yet you'd still flirt? I don't get it, Kate. Last week you were standing on a bomb, and you told me you loved me. You love me, Kate. And now you're flirting with some other guy. That's what I don't get. Were you just telling me that you loved me because that's what you thought I wanted to hear? In what were potentially our last moment together you wanted me to believe that you loved me. Was that it? Because, Kate, if you're just lying-"

"I wasn't lying! Castle – I wasn't just saying that because I was stood on a bomb. I didn't say it because I wanted you to believe that I loved you. I do love you. I love you so much it scares the shit out of me sometimes, but us, we solve murders, we come home, we have a bottle of wine and we go to bed and we wake up and we solve a murder and we come home, we have a bottle of wine and we go to bed and then we wake up and we do the same thing and I'm terrified that this is all we are. That we're not actually going anywhere, and Vaughn was new and he was exciting, and I wasn't thinking and I'm sorry."

"You don't think we're going anywhere?"

Kate sits on the edge of the bed, presses the heel of her hand into her temple. "I don't know, Castle. Maybe I'm just being ridiculous. It's not even been a year, but I just thought after everything we've been through then things would be different. If you're scared that I'm going to run, I'm not. You're my partner, Castle. And like Espo says, that means I'm with you until the wheels fall off."

There's the sound of movement behind her and then an arm wrapped around her arm, giving it a gentle tug backwards. She follows easily, ends up sprawled on top of Castle. "Vaughn is a dick. I hope you hit him hard."

"He's gonna have a black eye."

Castle laughs against the crown of her head. "Good. But you're with me until the wheels fall off?"

"Until the wheels fall off."

He's quiet for a few more moments, she can hear the cogs whirring and turning and clicking over as he thinks. "Move in with me."

Kate jerks her head up so fast her neck twinges, and Castle is staring at her with such sincerity that her heart pounds so hard against her rib cage she's surprised they can't hear it. "You're – are you serious?"

"Yes. You want it to go somewhere, I want it to go somewhere, so move in with me. You've already got some stuff here. Your alarm clock can go on the bedside table, and you can clog up the other chest of drawers with your many and various knick knacks. I'll move all of my stuff out of it, all your clothes can go in there. I'll make room in the closet. You don't need to worry about Gates finding out when you change your address. You've got a key already."

Kate stares at him for a moment, and then finds herself nodding. "Okay."

Castle's eyes light up, and he smiles at her. Cute, and shy and completely adorable. "Yeah?"

"Yeah. I'll move in."

Castle laughs, and she can't help but grin as she arches up to press her mouth against his. His hands are already tugging at the hem of the shirt, pulling it over her head and flinging it away from the bed.

Last ornament placed, all clothes put away, her shower gel is next to his in the bathroom. Her apartment is no longer hers. Officially moved out, officially moved in with Castle. It was tedious work, sifting through all the stuff she doesn't need (though Castle had always said she could just put in storage), but in the end she left about five boxes of stuff with a charity store just down the road. And now she's lying flat on their bed waiting for Castle to return with the champagne. It's been a month since she agreed to move in which is ridiculous and crazy because it was only a year ago, or there about, where she turned up rain sodden at his front door, unsure about whether he was going to reject her or just get her out of his veins so he can finally move on. And now she's living with him. Her clothes are in her drawers, and her pictures are dotted around the loft, her make-up shares a counter with all of his shaving gear. Her pillows have taken home on his armchairs in his office, her throw blanket is on the armchair next to her side of the bed. Completely at home.

"You know," Castle states, walking into the room with the bottle of champagne and two long flutes, sitting on the bed next to her prone form, "next time you flirt with a guy, I'm gonna have to ask you to marry me."