A/N: just to clear up the confusion of a guest reviewer - Lanie and Charlie hadn't met until now, but Lanie knew Charlie existed. Thank you all so much for the reviews - and the birthday wishes, you're all amazing! And here is my first chapter not being a teenager anymore ;)

PS: theres a couple of naughty words in this chapter, I'm leaving it as K+ but if you think it should be T then let me know and I'll change it! Basically just a little rude if you're about 12, any older and I'm sure you've heard worse!

Castle slipped out of the booth quietly, muttering something about getting more drinks. Kate watched him go, a slight frown forming on her face. Ever since their friends had arrived, Castle had been unusually quiet - not himself at all. Standing up, she followed him over to the bar and stood next to him.

"Hey," she said quietly, "you okay?"

"Yeah, I'm fine," Castle replied unconvincingly with a small smile.

"Uh huh, wanna try it again, make it sound a little more convincing?" Kate counteracted. She knew there was something bothering him and she was determined to get it out of him.

Castle looked at her. He wasn't fine, not really, he was upset and a little angry that Lanie had known about Charlie and he didn't. He knew Lanie and Beckett were best friends and they talked about things with each other that others didn't know, but this was pretty big. Four years they'd been working together and the whole time her and Lanie had known Charlie was out there and he hadn't been trusted with that information? Was she worried Nikki Heat would end up with a twin sister too or something?

"Okay, you're right, I'm not fine," he hissed, hoping their friends - and family in Kates case - were still engrossed in conversation enough to not realise he and Kate were about to have a fight in the middle of his bar. "I'm angry, actually. Angry that you trusted Lanie with the fact that you have a twin but not me. Worried I couldn't keep my mouth shut? Worried I'd have Nikki Heat with a twin sister too? Or were you worried I'd prefer her to you? Is that it, Beckett? Is that why you didn't tell me? You thought I'd meet Charlie and realise she's not as emotionally damaged as you?" He'd gone too far and he knew it the moment the words left his mouth. He should have stopped at the Nikki Heat thing but he was angry and he'd blurted out the words before he realised what he was saying.

Beckett stared at him shock for a moment before turning on her heel, striding back over to the table to grab her bag and marching out of the bar. Castle didn't even have a minute to figure out what had just happened before Lanie and Espo were demanding to know what he'd done.

Castle couldn't help but notice that the one person not looking at him like he'd just kicked a puppy was Charlie. He turned to her wearily and said, "shouldn't you be hanging me up by my balls or something right now?"

"What, for pissing Kate off? Jeez, if someone berated me every time I managed to do that then I wouldn't have come home," Charlie said, sending him a reassuring smile. The two of them had moved away from the others, standing at the bar where he and Kate had been just a few minutes ago. "Look, the reason you can piss her off that much is because she cares, okay? I don't know what you said to her, but I can pretty much guarantee that if it had been practically anyone else, she would have replied with some witty remark and not let it get to her. But this is you, whatever you said got to her.." She trailed off, wondering if Castle was actually going to tell her what he'd said to Kate.

Castle sighed and ran his hand through his hair. Just when he thought they'd been getting somewhere, he screwed it up again. "I was annoyed that Lanie knew about you and I didn't. I asked her if it was because she thought I'd prefer you.." Castle winced as he repeated his own words, he could see now why she had stormed out in such a huff.

"Ah," Charlie said with a grimace, "well, I can kinda see where she's coming from.."

"Yeah..oh god I've screwed up so bad," he groaned,sinking his head into his hands.

"Well yeah, you have but she'll come around, she's put up with you for this long hasn't she?" Charlie teased, trying to lighten the mood.

"Mm yeah, I guess she has. I mean I didn't think she'd ever talk to me again after I-" he stopped myself just in time. Hadn't Beckett said Charlie didn't know about the advancements in their mothers case?

"After what?" Charlie said, narrowing her eyes at him in a way that Kate did at least once a day.

Castle hesitated. He didn't want to tell Charlie everything, Kate was angry enough at him already. But he could tell her the basics without giving anything away, right? "I uh, looked into your mothers case after she specifically asked me not to," he admitted.

To his surprise, Charlie laughed, "oh god, I bet she was so angry with you!" She knew what it was like to be on the receiving end of a pissed off Kate Beckett and it was not something she envied.

"Yeah, she was.."

"But she forgave you," Charlie reminded him, adding because she loves you silently. "And she will again, you just need to give her time. Anyway, what happened when you looked into moms case?"

Crap. What did he say now? 'Oh yeah, by the way we caught the guy who killed your mom and he was about to get away but Kate shot him. And now I'm doing my best to keep her safe from whoever the hell wants to kill her but she doesn't know about it, so that's probably another reason she's going to hate me forever.' Yeah, or not. "I um, think you should ask Kate about that.." He evaded, desperate to stay out of this the best he could.

"Castle," she warned, in a way that reminded him scarily of Kate.

Well, he was really in trouble now. "Look, you need to talk to Kate, okay? It's not up to me to tell you."

Charlie could see she wasn't going to get a straight answer out of Castle and made a mental note to ask Kate about it later. "Right, well come on, let's get more drinks."

"No you're alright, I'm going to go home, figure out how the hell I'm going to make this up to her.." Castle said gloomily.

"Okay," Charlie smiled. "She'll come around, I promise."

Castle shot her a small smile and said goodbye to the others before heading out into the late afternoon sunshine.

Castle was halfway back to his apartment when he changed his mind. Leaning forward, he asked the cab driver to turn around, rattling off Beckett's address instead. Screw giving her time, he'd given her four years of fucking time, he needed to apologise and he was going to do it now whether she wanted him to or not.

Standing outside her door, he ran his hands through his hair and knocked, nervously waiting for her to answer. The door swung open and then almost completely shut again when she saw who it was but he stopped it with his foot.

"Beckett, wait, please," he pleaded, "just let me explain."

He sensed her hesitation and used it to his advantage, pushing the door gently until it was opened wide enough for him to enter her apartment. She sighed and spun around, retreating away from him, clearly still angry.

"Beckett..Kate..I'm sorry."

"Great, now you can go," she replied sharply, not even bothering to hide the fact she quite clearly didn't want him here.

"I'm not leaving until I've explained and you understand," he said, standing his ground. He came here to give her an explanation and that's what he was going to do, even if it took him all night.

"Do you want me to arrest you for stalking or..trespassing or something?"

She was sexy when she was angry. The way her eyes narrowed at him, the scowl on her face..all of it, she was so fucking hot and damn near irresistible. "Anyone ever tell you that you have a smart mouth?" He quipped, grinning at her.

Damn him and his stupid blue eyes and his charming smile. God the man was infuriating but no matter how much he'd pissed her off earlier, she was still completely and utterly in love with him. Dammit. "Just pointing out the facts, Castle," she replied. "I'm not going to get rid of you am I?" She asked and he shook his head. Rolling her eyes, she said, "okay then, out with it, say whatever it is you came here to say and then you can go."

Castle was suddenly lost for words. He opened his mouth a few times but promptly closed it again when he realised he had no clue what to say.

"You came here to impersonate a goldfish?" She asked, a grin pulling at the corners of her mouth.

The sass was back and he'd be lying if he said it wasn't a complete turn on. He was flooded with visions of her muttering smart ass comments in his ear before he made her forget her own name, never mind what she was saying. "Very funny," he replied, "no, I came here to say I was sorry and I didn't mean what I said. It was out of order and I shouldn't have said it and I apologise."

He sounded so sincere that she almost told him to forget it and that it was fine, but she was still a little hurt at his comments and she wanted to know why. "So why did you say it then?" She asked quietly.

"I was angry. I could just about cope with you not telling me about Charlie if no one knew, but then Lanie came in and it turned out she'd known all along. I know she's your best friend and the two of you have secrets together, but I guess I just felt that you didn't trust me enough or something." He was perfectly aware that he sounded like a fifteen year old girl with a crush right now but he didn't care, he needed her to forgive him - preferably before she found out he'd brought up their moms case with Charlie.

"You were right to be angry. I should have told you, I know that, but please Castle, please don't you ever think I don't trust you because I do, more than anyone I've ever met and sometimes more than Charlie."

"Come here, you," he said, pulling her into his arms and wrapping her into a tight hug. "I know you trust me okay?" He felt her nod against his chest. "You mean a hell of a lot to me Kate and I'm so sorry for what I said, because I can promise you that Charlie could walk in here in her sexiest underwear and I'd still want you in your sweatpants. I'm not going to lie and say she's not hot cause that would just be stupid," he heard her chuckle slightly and he smiled. "But I want you Kate, only you."

"Castle, I-"

He hushed her before she could finish, "ssh, Kate, it's okay. I know you're not ready to hear that and I've accepted it. I'm here whenever you need me, okay?"

Kate didn't know what to say. Before he had stopped her, she was on the verge of telling him she loved him but then he had stopped her. It wasn't necessarily the fact that he had stopped her, more the fact that he had said once again that he knew she wasn't ready. When she told Castle how in love with him she was, she needed him to know she meant it and right now, just after he'd said he understood she wasn't ready, didn't seem the right time.

But how much more time did she have? Four years they'd been doing this dance and the music was about to stop. She wasn't too sure how much longer she could fight these feelings she had for him. And like Charlie had said, he wasn't going to wait forever.

"No, it's not that," she began, "it's-"

"Oh there you are I've been calling your phone for ages! Oh, sorry, did I interrupt.." Charlie called out as she entered the apartment using the spare key Kate had given her.

Kate could have murdered her - she was sure Castle would help her hide the body. Talk about bad timing! She couldn't wait to tell Charlie about what she'd just interrupted..

"Well, given that you aren't shouting at each other I'm assuming you sorted things out," Charlie stated before turning to Castle. "See, I told you she'd forgive you! Oh, actually seeing you reminded me - Kate, what haven't you told me about moms case?"

Kate's eyes widened in shock before narrowing them at Castle.

Oh crap, he thought, maybe she had forgiven him too soon.

"Castle.." She said, "what did you say?"

A/N: anyone notice the KB line I stole from 5x02?! This is taking a slightly different turn to how I planned it, but I hope you're all still enjoying it!

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