A/N: after talking to a few of you about the last chapter, I think I've realised why I didn't like it - I had it all planned out and then I went and watched the finale and just couldn't bring myself to write it anymore! So, I'm changing my mind and taking it a different way!

I have now planned out what is potentially the final four chapters - I really don't want this to end but I also don't want to drag it out and it end up being boring etc. It is going to have a proper ending though, I'm not leaving it like this!

It was dark. That was her first thought. And it smelt - bad..sort of like a mixture between a sewer and vomit, definitely not pleasant. She could also sense damp..like she was in a basement or something. Her head felt heavy and fuzzy, but she forced her eyes open anyway, willing herself to focus, determined to work out where she was and how on earth she could get out of this situation.

The next thing she realised was that she was sat on a hard wooden chair, with her wrists and ankles tied with a rope to the arms and legs. Well, that certainly wasn't a good start. Her eyes had adjusted to the darkened room and she glanced around. From what she could make out, she was sat in the centre of a basement - there were no windows, just a door in the left hand corner which she presumed led up to the main building.

But why? Why was she here? The last thing she remembered was leaving Ethan's office to go and meet Kate and Rick..she'd hailed a cab - she'd been surprised to get one so quickly in the busy New York traffic..wait, that must be it - she didn't remember anything after getting into the cab, she must have been taken by whoever was driving it! That still didn't explain why, though..why would a cabbie take her hostage?

Pulling on her restraints, she soon realised she wasn't getting out of them - they'd been tied by a professional, whoever had brought her here had done this before.

Panic ripped through her, despair at not knowing where she was or why, even worse with no obvious way out. Her mouth wasn't gagged, though, but she didn't know if she dared to call out, she didn't know what was waiting on the other side of that door.

Her only hope was her sister - Kate was the best detective in the city and she was bound to know when Charlie didn't turn up for lunch that something had happened. She just had to hope Castle kept Kate calm enough to do her job - and find her.

"So, is Cole Maddox your real name?" No answer. He'd said nothing as Kate had arrested him and in interrogation now he still wasn't talking. "Do you know who I am?" She asked. They were pretty certain that this was the guy who had tried - and almost succeeded - to kill her at Montgomery's funeral last year, but he still didn't reply, didn't even move. "Let's try this - who do you work for?" It was a ridiculous question, Dick Coonan hadn't given it up so why would this guy? "Okay, you're not talking, fine. I'll just leave you to sit in here for a bit, let us know if you remember your name or something." Kate gathered up the files and walked out, heading into the observation room.

"It's him," she said to Castle. "And I know he knows who I am..god this is so frustrating!"

"Hey, don't worry, okay?" Castle reassured. "If something has happened to Charlie and it's him that's got to her then at least if he's here then he isn't hurting her, right?"

"Unless he's already-"

"Don't," Castle warned. "Don't think like that, okay? And besides, that's not his MO - it's you he wants dead, not Charlie. He'd need Charlie alive to get information - and I'm pretty sure he knows if he hurts your sister then you'll go in there and put a bullet through his skull."

"What would I do without you?" Kate muttered, leaning into his chest. Luckily they were alone in there, Espo and Ryan were going through evidence from his hotel room, seeing if they could find anything.

"Have him up against the wall by his balls, I would imagine," Castle chuckled. He knew she must be worried - he was too - but he really believed what he'd told her - Maddox needed Charlie alive to get to Kate. And either Maddox was a really good actor or he knew Kate and Charlie were identical, he'd shown no surprise at seeing Beckett.

"I'm gonna give it another shot, see if he'll talk this time."

"You want me to come?" Castle asked, despite knowing the answer already. She'd asked him to stay behind the glass the last time she went in, thinking it would be better for her to question him alone. But he had to ask, he knew Beckett - if she wanted him in there this time, she wouldn't ask him, she'd wait for him to offer.

"Please," she replied quietly, surprising him. "I need someone to stop me having him against the wall by his balls."

"Come on then, let's get this scumbag."

Castle could have sworn he saw a hint of a smile gracing Maddox's lips as they walked back into the interrogation room. "We have forensic officers searching your hotel room from top to bottom, you know," Kate said lightly as they sat down opposite him. "And the second they find even circumstantial evidence, it will be enough to book you on. Maybe you should start talking."

"I have nothing to say," Maddox said. "And your officers aren't going to find anything. You may as well stop wasting your time and let me go."

Well, at least he was talking now. Before either of them could speak again, they were interrupted by a knock at the door. Esposito walked in and handed Beckett a file, which she opened, a small smile forming on her face. "So, Mr Marks, is it?" She said and even Castle saw Maddox flinch. "Oh, so you weren't expecting us to find your real identity, no? Anyway, now that we're all familiar with each other, why don't you start with telling me where the hell my sister is?"

"I don't know what you're talking about," Maddox replied calmly.

"You know exactly what I'm talking about and it's not going to be long before CSU find me some proof." That was a lie - CSU should be done by now and they hadn't given her anything that proved he had Charlie, nor that he was the one who shot her and no clues as to who he was working for. "Are you sure you don't want a lawyer?"

"I don't need a lawyer because in about ten minutes time you're going to realise you have nothing to keep me on and have to let me go."

It was true, both Castle and Beckett knew that. They had nothing and he knew they couldn't keep him, not without probable cause and no evidence. "Okay, we'll play it your way," Beckett announced, a lot brighter than she felt. She gathered up the files once more and headed back towards the door, Castle just in front of her.

She stopped in her tracks as Maddox spoke once more. "You have no idea who you're going up against, Detective, but you better stop before you - or your sister gets hurt."

It was only Castle firmly grasping her wrist that stopped her charging over to him and slamming his head into the table. "We'll see about that."

"We've got to let him go," Beckett sighed to Castle, Espo and Ryan. "We've got no proof and he knows that."

"But..he practically just admitted to having Charlie!" Castle spluttered.

"He didn't admit it directly, though," Beckett said. "If I tried to keep him on that then any defence lawyer worth their dime would come back with it being because I suggested something had happened to Charlie in the first place. If I hadn't asked him..well then I could keep him, but I can't, not now."

"But you think he has Charlie?" Ryan asked.

"Pretty certain of it," Beckett nodded. "But I can't prove it." The four of them watched in disgust as two uniformed officers uncuffed Maddox and led him to the exit, the dirtbag not even bothering to hide the smirk on his face. "I'm going after him," Beckett announced.

"Uh, no you're not!" Castle counteracted and the other three turned to stare at him.

"Excuse me?" Kate asked, raising an eyebrow, quite clearly expecting him to stand down and cower away from her look.

"You're not going after him!" He reiterated, standing his ground.

"And that's our cue to leave," Ryan muttered as he and Espo shuffled away. Neither of them particularly wanted to get in the middle of a Castle and Beckett fight.

"And why, may I ask," Beckett continued, "have you suddenly decided you can tell me what to do?"

"It's not like that and you know it," Castle scathed. "I'm not telling you what to do, I'm just saying that going after Maddox isn't the best idea! He's already tried to kill you once and the only reason he hasn't over the past year is because you weren't looking into it!"

"Well he already knows I'm back on the case, and he has my sister - so whether you like it or not, I'm going after him!" Beckett shot back, trying to keep her voice down so as to not draw attention from the other detectives.

"Well at least do it properly!" Castle pleaded. "Bring Gates in on it and have her send back up with you!"

"And have her throw me off the case? No, I don't think so somehow. I'm doing this and I'm doing it my way. Besides, you really think a trained killed like Maddox isn't going to spot a swat team a mile off? It's a ridiculous idea, he'd run the second he spotted us and goodness knows what would happen to Charlie! This is my sister we're talking about, Castle, you can't expect me to just sit back and wait for something to happen!"

"Please, Kate," Castle begged. "Please just think about what it is you're doing - you say you're doing this to protect Charlie but what's to say he isn't going to kill you first?" He took a deep breath before continuing. He really didn't want to use this against her but right now he had no choice. "You told me you would always choose me over your mothers case."

"Don't you dare, Castle," Beckett hissed. "Don't you dare. I meant what I said but this isn't the same thing. My sister is out there somewhere, god knows where, probably alone and quite possible hurt or injured."

"So you're changing the rules so it suits you? No change there then," he spat out before walking away from her. "Go do what you want, Beckett, it's not like I could stop you anyway."

"Castle.." She called out but he was already gone, not looking back. She was torn - choosing between her twin sister and the man who had stolen her heart was a choice she never thought she'd have to make. She meant what she'd said when she told him he would always come before her mothers case, but she still believed this was different - how could he think she'd step back and wait while her sister was missing? She had to go after Charlie and informing Gates was not an option, not if she wanted to stay on the case and keep her job.

Castle was bubbling over with anger as he exited the elevator and headed out onto the street. He knew she was worried and he knew she just wanted Charlie back safe and sound but she wasn't going the right way about it. He had watched her die in that ambulance a year ago and knowing it was the same person behind this who shot her was driving him insane, why couldn't she just listen for once in her goddamned life?

All she had to do was tell Gates what had been going on and they'd have a surveillance team on Maddox faster than you could say Nikki Heat, it wasn't rocket science! And yeah, Gates would probably pull her off the case but surely that was better than going after him alone and possibly getting herself killed trying to get to Charlie? For someone who was so intellectually smart, she was incredibly stupid sometimes, damn stubborn woman.

He hadn't been paying attention as he'd left the precinct, so caught up in his angry thoughts about Beckett. He found himself outside one of their favourite coffee shops, staring up at the sign. Deciding coffee might give him something else to think about for a while, he headed inside and ordered. It was while he was waiting for his order that the idea came to him - Beckett might not be telling Gates what was going on but there was nothing stopping him and the boys telling her. Beckett would probably shoot him the second she found out but as long as her and Charlie were okay, he didn't really care. Finalising his decision, he took his coffee and made his way back to the precinct - narrowly missing Beckett as she went on her mission to find Maddox and her sister.

After Castle left the precinct, Kate tracked Maddox's cell phone using the GPS signal and hurried into the elevator to find him before he moved on again. She was hoping he didn't think anyone would be following him and that he'd lead her straight to Charlie, but she knew there was a chance he could be onto her and lead her somewhere completely different. She had to take the chance though, just in case he was where he was keeping Charlie.

Pulling up a block away from where he was supposed to be, she walked the remaining distance and found herself outside a small apartment building, which looked to be unused. There was no doorman and the door was still open so she headed inside, still checking on her cell where the strongest signal was coming from. She was halfway up the stairs, the signal getting stronger with each step when a thought crossed her mind - he might be upstairs, but she should probably check the downstairs first, just in case. Gun drawn, she slowly made her way over the door under the stairs, thankfully finding it unlocked.

It was dark, but she had her torch with her. Shining it forward, it allowed her to see a set of stone steps, leading down to what she assumed was the basement. Following it down, checking behind her as she went, she almost cried out with relief to find Charlie in the centre of the room, tied to a chair.

"Oh thank god," Beckett breathed, rushing over to her sister. "Are you okay? Did he hurt you?"

"No, I'm fine," Charlie gasped, her relief evident on her face. "We need to be quick, he's only going to be upstairs for a minute, he said something about taking me to DC? Who is he, Kate? The last thing I remember is hailing a cab to come and meet you and Castle for lunch and I woke up here!"

Kate quickly untied Charlie's restraints. "He's the guy who tried to kill me last year," Kate admitted. "He's after me again after this deal Castle made was broken, seems he was using you to get to me. I'm so sorry, Charlie."

"Hey, you don't need to apologise!" Charlie said. "I'm fine, okay? So let's get out of here!"

"Good luck with that," a voice sneered from the top of the stairs.

Kate drew her gun again and aimed at the shadowy figure, but he was too quick for her. He dodged her bullet before returning fire of his own - luckily Kate had managed to untie Charlie completely and the two of them could hide from him slightly. "Come on, Detective, you can do better than that!" He called and Kate aimed at him again.

"Right," she whispered to Charlie. "I'm going to go after him - when I've got him out of the way, you run out of here and call it in, okay? I should have called for back up but I was so relieved at finding you it completely slipped my mind."

"Wait," Charlie hissed back, "he's dangerous, shouldn't we wait for back up before you go after him?"

"And risk having him shoot the pair of us before I can call it in? No, it won't work, this is the only way. Take this," she handed Charlie her radio. "When you get outside, press the button on the side and tell dispatch that Kate Beckett, badge number 41319 has apprehended a suspect. Give the address and tell them back up is needed urgently, the suspect is armed, okay? Right, on my count. One, two.."

On three, Kate jumped out from where her and Charlie were hiding and shot at Maddox again. She couldn't see much, but judging from the gasp he made before backing away slightly told her she was close. She creeped up the stairs, keeping her eyes open for any movements. He reacted quicker than she thought he would and she only just flattened herself against the wall in time, his bullet landing somewhere down in the basement.

Looking up again, she saw him disappear behind a door, one she was assuming led to a staircase. She could drop it now and take Charlie outside, call for backup and have them deal with it - that's what Castle would want her to do, anyway. But she couldn't. A whole year had passed since she'd been shot and they'd had no leads for eleven months, this was her best chance of getting him and finding out who was behind her mothers murder. Satisfied that Charlie would be safe now, she followed Maddox through the doors and started climbing the stairs.

There was no sign of him until she reached the roof. He took her by suprise, grabbing her from behind. She struggled to get out of his grasp and he threw her to the ground, landing on her back with a groan. Before she even had time to work out another move, he grabbed her by the throat and pulled her up, squeezing just tight enough that she struggled to breathe. Hitting him as hard as she could, she used it to her advantage and wormed herself out of his grasp as she hit him. Falling to the ground, she desperately tried to catch her breath, seriously hoping Charlie had called for backup and they weren't far away.

"Just tell me who's behind this?" She pleaded.

"You're wasting your time, detective, you have no idea what you're up against."

"Neither do you." She lunged for him but he was so much better than her, a trained killer who had learnt the hard way how to fight. Before she knew what was happening, she was hanging off of the building by her fingertips.

"Actually, we know exactly who we're up against," Maddox said, starting down at her before walking away.

Dammit Castle was right. She should have done as he suggested, tell Gates what was going on and let them deal with it properly. Charlie would be safe and she wouldn't be hanging onto a building for dear life.

"Help!" She called out, hoping Charlie might hear her. Looking down, she almost fell right then. It was a hell of a drop and with the busy traffic a steady hum below her, Charlie wouldn't be able to hear a thing. She just hoped Maddox hadn't gone back after her. "Castle," she whispered, one hand slipping off the edge of the building. "Oh god no. Castle!" She called, a little louder this time and she could swear she heard him reply.

"Beckett! Hang on Beckett!"

"Castle? Oh god, Castle, I'm here!" She cried, fingers slipping further off the edge. "No..come on! Castle!"

"Beckett?" He called once more and her fingers slipped further. Oh god, this was it, she was going to- "Beckett!" Castle shouted, his wrist gripping hers and hauling her back up onto the building. "Oh god, Beckett!"

"Castle?" She asked, unsure it was really him.

"Yeah, it's me," he smiled. "God, you had me so worried!"

"Charlie?" She gasped.

"Is fine," Castle reassured and Kate looked over his shoulder. Charlie was stood there with Ryan and a couple of swat team members.

"How did you get here so fast?" She asked. It hadn't been that long ago that Charlie could have called it in, they couldn't have got here as quick as that..

"I uh, might have um..told Gates.." He stuttered, not meeting her eye. "She tracked Maddox and we guessed that's where you'd gone."

He did what? Oh she was going to kill- wait, if he hadn't told Gates, she'd probably be dead. "I guess I can let you off considering you saved my life and all," she relented.

"Thanks," he replied, grinning sheepishly.

"But uh..I thought you'd given up on me.." She said, "when you left.."

"I was angry, Beckett, but I wouldn't give up on you, I couldn't."

She really didn't deserve him, she knew that now more than ever. "Thank you, Castle."

"Always," he replied and she grinned, leaning in to kiss him, soft lips meeting in a frenzy. He deepened the kiss, slipping his tongue past her lips and-

"Ahem," a voice interrupted. The two of the broke apart, searching for the owner of the voice - it was Gates and she didn't look happy.

"Detective Beckett, the second you get back to that precinct, I want you in my office, is that clear?"

"Yes, sir," Kate replied quietly, looking at the ground. She was in serious trouble now.

A/N: let me know what you thought :)