A/N: I know, I know - I'm a nightmare. Yes, I'm starting another story. BUT Wedding Speeches is now complete and Trained to Kill will be finished in the next couple of days as I only have one more chapter to write. This idea literally just came to me and I got so excited that I HAD to write the first chapter. I'm not sure how long it'll be yet, guess it depends if you guys like it!

Summary: AU. Kate Beckett has a secret. And that 'secret' is coming to town. When Kate and her 'secret' devise a plan, all sorts of things could happen - especially when the subject of their plan is the one and only Richard Castle.

Timing: probably mid-end S4, but before Always.

Kate's phone beeped, alerting her to a new text message. Pulling it out, she unlocked her cell and read the message: "My flight gets in at 1pm your time on Friday - that's three days from now, in case you'd forgotten. I expect to see you there with a welcoming party of some sort - can't wait to see you! Xox" Kate smiled before sending a text back saying that she would be there on time and waiting. Putting her cell back in her pocket she bit her lip, contemplating on how she was going to handle this situation.

The thing was, Beckett had a secret. A huge secret, even Castle didn't know. The only person who knew was her dad and that was for obvious reasons - Katherine Beckett had a twin sister. An identical twin sister, seriously, unless you knew either of them inside out, you wouldn't be able to tell the difference between them by looking at them. However when it came to their personalities, they were the complete opposite. Where Kate was fairly quiet and reserved, her twin was loud and boisterous. Kate had trouble putting her feelings into words - or actions - something which her sister had no problem with doing. They were literally like chalk and cheese.

Kate hadn't seen Charlie - short for Charlotte - in almost five years. Charlie was an English teacher to children in third world countries. She'd moved to London after finishing her degree and spent three years working in a boarding school over there before heading to countries such as Vietnam, Cambodia and Thailand.

The last time they'd seen each other was when Kate was sending her other half off to England and they hadn't spoken much since. They had been inseparable as kids but when their mother died, they'd taken it in different ways. Where Kate had thrown herself into the investigation and joining the force, Charlie had let bygones be bygones and accepted the fact they nothing they did would bring their mother back. At first, it had caused huge arguments between them but they finally accepted to not bring it up around the other - it had never been the same though. However, with Charlie having been gone for five years and the two of them hardly talking in that time, Kate felt like it was time to see her sister again. They'd sent a couple of emails back and forth a couple of times a year - their birthday, moms birthday and anniversary, but apart from that - nothing. They had a lot of catching up to do when Charlie got home.

She hadn't said how long she would be back for but Kate was hoping to convince her to stay for good. She'd missed her and wanted her home and safe, she could teach English here, with her experience she'd get a job anywhere.

Kate's other problem right now was how she was going to tell Castle - he'd based a character on her, knew pretty much everything about her moms murder, spent day after day at her side and yet he didn't know she had an identical twin. That was going to be a fun conversation.

Unfortunately, Kate never got the opportunity to tell Castle about Charlie. They had three bodies drop within five hours and what had first seemed like three separate homicides, had all ended up being connected. It had been Castle that had made the connection - much to the disbelief and slight annoyance of Captain Gates, she really didn't like him.

So here they were, their suspect had just lawyered up - quite likely suggesting he was guilty. They were just waiting for the lawyer to arrive so they could interview him again when an officer from downstairs called out to Kate.

"Yo, Beckett, I've got a Charlie downstairs, said you should know her and that you were supposed to meet her?"

Crap. Kate looked at her watch - 2.30pm. On Friday. She was supposed to have picked Charlie up from the airport an hour and a half ago. And oh god now she was going to have to explain to Castle and the boys what was going on.

Before Kate could respond, the elevator doors opened again and out walked Charlie - and she did not look happy. She strode over to Kate's desk and Castle swung around to see what had Kate looking so worried.

Turning back to her, he said, "either I'm seeing double or that woman is the spitting image of you."

Unfortunately, Charlie heard this. "Spitting image? Of course I am, she's my twin sister."

Castles eyes widened and his mouth opened and closed a few times before he managed to get any words out. "Twin..sister?" He said, looking at Beckett. The first one.

Kate nodded. "Uh, yeah. Charlie, this is Richard Castle, my partner. Castle, this is Charlotte, my annoying twin sister."

"It's Charlie, not Charlotte," Beckett two said, holding out her hand for Castle to shake. "Or do you want me to revert to calling you Katherine?"

"My mother calls you Katherine," Castle stated, still looking like he was dreaming or something.

"Yes, and when she does it, it's sweet. But when Charlotte here does it, I know it's to annoy me. When we were younger, it was only ever Katherine if I was in trouble."

"So," Charlie said, sinking into a spare seat next to Kate's desk. "You're that sort of partner, hey?" She assumed when Castle had mentioned his mom calling her Katherine, that they were more than just cop partners.

Kate answered "no," at the same time Castle said "not yet." Charlie watched them in amusement. This was not the same sister she had left behind five years ago and she was willing to bet Castle had had something to do with that. "So I take it from the look on your face right now that this delightful detective didn't tell you she had a sister?"

"No," Castle said, looking to Kate. "She didn't," he arched an eyebrow, waiting for an answer that would make all of this make sense.

"Oh god, I need coffee," Kate grumbled. She checked her watch again - 2:45. Their suspects lawyer still wasn't here yet and she hadn't had lunch. "We're going to Remy's, we can talk there," she announced to Castle and Charlie. She grabbed her things and popped her head into the tech room to tell Espo and Ryan that her and Castle were heading out for an hour for lunch. She didn't tell them about Charlie, she'd do that one person at a time - starting with Castle.

Ten minutes later and the three of them were in a booth at Remy's, having ordered coffee and burgers all around.

"So," Castle said, "you gonna tell me why you failed to mention for the past four years that you have a sister?"

A/N: so I know Beckett having a sister has been done before, but I've got a little something up my sleeve - this 'plan' should make it different when it materialises ;) anyway, please review this chapter - I'm kinda excited about it but that could just be me, please let me know your thoughts and whether I should continue! I know this chapter is pretty short, but I just wanted to see the general response I got before writing longer ones!

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