Hi all! This is my first ever fan fiction, am a bit nervous! I have a storyline all planed out and will be posting new chapters as they are completed. Lots of Casketty angst with romance ensuing! I have rated M mostly for future chapters but also for language throughout. I don't own Castle or any of the characters, I'm simply borrowing them to have some fun with!

I hope you enjoy, please give feedback!

**Chapter 1- Misunderstanding**

Kate smiled up at the ceiling, Saturday! The sun was streaming through her bedroom window, lighting the room with a warm glow that promised a beautiful day ahead. This was her first full weekend off in...well she couldn't remember how long and she had been looking forward to it. The captain had given her and her team the two days off in honour of Detective Ryan's Bucks night and his fiancée Jenny's Hens night. To top things off the previous day they had managed to close a particularly gruelling case, meaning they could all enjoy their weekend off without anything worse than paperwork waiting for them. And that was why at 8.30am Kate Beckett was still in bed, not thinking about bodies or cases or anything at all work related, just enjoying the morning and looking forward to the evening that was coming. On her bedside table her phone buzzed to life.

"Hey Josh," she smiled into the mouth piece.

"Hey babe," she cringed, it seemed she was going to have to address the pet name thing again. "So I have a few hours before my next surgery, thought we could catch up, maybe have lunch. What are you doing right now?"

"Still in bed," she replied guiltily, knowing Josh never got to sleep in, or sleep much at all for that matter. "Buuuttt...I suppose you join me," she smiled again, already knowing the response she was going to get.

"Don't move a muscle," she could practically see the grin on his face.

Kate did of course move a muscle, probably all of them in fact. She rushed to the bathroom, predicting it was approximately a twenty minute journey from Josh's hospital to her apartment. She pulled her hair into a messy bun to keep it dry as she hurried under the shower. Kate closed her eyes and relaxed as the warm water washed away all traces of sleep. She lathered the washer in her favourite cherry shower lotion and ran it over her arms, up her neck, across her chest, stomach and down her legs. As she rinsed she watched the foam pool around her lacquered toes and swirl down the drain. Regretfully she turned off the heavenly stream of water and stepping out of the shower, reached for a white, fluffy towel.

She dried herself off in front on the mirror, watching the steam rise as her warm body was met by the cool air the bathroom. Kate brushed her teeth and put on the tiniest amount of makeup, nothing too obvious. After a squirt or two of deodorant and a couple of sprits of perfume she pulled the tie from her hair and let her long brown locks fall messily around her shoulders. She ran her fingers roughly through the tangle, not that anyone else would see it as such, and gave up on it. She slipped into a fresh set of pyjamas. Light blue shorts with small green stripes running up her thighs and a green tank top which scooped low at the front and clung tightly in all the right places, all two of them anyway.

Before hopping back into bed she unlocked her apartment door and grabbed a book. Propping herself up on her pillows and opening the novel to a random page she attempted a 'what? I always look and smell this good when I wake up', not that he hadn't seen her first thing in the morning before, but still. Things had been weird between them for a while, a long while in fact, and when they did finally get a few minutes together she tried to make a bit of effort.

She heard a loud knock at her door, "it's open," she called out, putting her nose in her book and pretending to read casually. She heard the door open, "I'm in here."

"Detective, I know you sleep with a gun and all but really, I could have been anyone!"

Kate froze...Josh did not call her 'Detective' and that was not Josh's voice.

"Castle? What are you doing here?" she hissed as he appeared in her bedroom doorway.

"You invited me in," he replied grinning at her propped up in bed, she noticed him eyeing the low neckline of her top. "Do you always look and smell that good when you wake up?"

"You have to go...now Castle, right now!" oh God, if Josh walks in to Castle here he is gonna freak.

"I only just got here," he whined.

"Seriously Castle. You can't be here."

"I just wanna talk to you about tonight."

"Castle, Josh is..."

"Kate?" Fuck! At first Josh sounded confused, probably wondering why there was a man standing in his girlfriends' bedroom, until he saw who the man was, and then he just sounded pissed. "What the hell are you doing here?"

Castle had spun to face Josh as soon as he heard him call her name. Neither of them had heard him enter her apartment probably coz he didn't knock...another thing to mention!

"Hey Josh," Castle responded cheerfully, not sounding at all guilty and not answering his question.

"I said what the fuck are you doing here?"

"Josh!" Kate warned, starting to move out from her bedcovers, though feeling very conscious of the fact she was in her pyjamas.

"What the hell is this Kate?"

"Sorry man, just a little misunderstanding, I knocked, she obviously thought I was you..." Josh cut him off.

"Misunderstanding my ass. Are you fucking him Kate?"

"Oh my God, Josh!" Kate yelled at the same time as Castle said, "Woohh Josh, calm down!"

Before Kate realised what was happening Josh slammed Castle against the wall, balling his fists around handfuls of Castle's shirt. "Don't tell me to calm down," he yelled into Castle's face.

Kate had seen Castle take crooks down a number of times, mostly when they had threatened her life or put her in danger, so she knew he could drop Josh. But he barely reacted at all, just watched him carefully as Josh grew angrier and angrier.

Kate, crossing the room to the two men pulled at Josh's arm, "Let him go Josh." He refused to let up on his grip on Castle. Instead he shouldered her away from them, sending her stumbling into the opposite wall. Castle did react then. He very swiftly took hold of Josh's collar, shifted his leg to behind the other man and easily deposited him on the ground at his feet where he sat, breathing heavily and glaring daggers at them both. Josh was fuming, but so was Kate.

"Josh, you have no right to come in here...in to my apartment, and abuse my partner, who was doing nothing wrong," she shouted at him.

"You have no right to be slutting around with other guys while you're in a relationship with me!" He retorted.

Kate blinked, Josh was suddenly lying sprawled on the floor with blood pouring from his face, Castle was grimacing and massaging his right hand with his left. Josh looked as confused as Kate, but realisation was dawning on him quickly and he struggled to get up.

"Stay there Josh," Castle ordered. Josh of course ignored him and pushing against the wall her raised himself on uneasy legs.

"Castle I think you should go," Kate suggested weakly, her mind attempting to piece together exactly when Castle had punched her boyfriend...ex-boyfriend, and wondering how her morning had gone so horribly wrong.

"There is no way I'm leavening you with this psycho!"

"I'm her boyfriend," Josh spat.

"No you're not," Kate said simply.

"Kate? What the hell? I haven't done anything wrong. If anything I should be dumping you. You're the one cheating."

"Josh if you think...I'm not going to tell you again..." She took a deep breath, "you know what? Fine dump me, I don't care who does the dumping, so long as when you leave this apartment you understand we are over and you never come back." Kate noticed Castle was watching Josh carefully.

"It's okay Castle. Josh is leaving now."

"Ahh...No I'm not, we have to talk. We can get through this." He said and Kate realised how much of an idiot he was.

Before she could say so Castle spoke up, "she said she wants you to leave. Get out," Castle said quietly, dangerously his blue eyes burning with suppressed rage. Josh rounded on him again.

"Castle please?" Kate begged, he really wasn't helping, he was only going to make Josh madder.

"Listen writer, this is my girlfriend. You are the one who needs to leave. And I think it's best you find someone else to follow round. Coz you two are done."

"That's it, Josh, get the hell outta my place. We are done. You have to leave right now."

Josh advanced towards her anger burning in his eyes, his mouth twisted, "I say when we are done. This is all your fault and I will not leave. You are mine and I won't let you fuck around with anyone else."

Kate saw it happen this time because this time she was expecting it. Castle seemingly out of nowhere had Josh by the back of his shirt and was throwing him out of her bedroom. He crashed into the hallway wall, swearing at the top of his lungs. Castle followed him out and Kate was close behind. She watched as Josh launch himself at Castle, knocking him into the wall, saw him punch Castle in the side of his head, and watched as Castle staggered. He recovered quickly and threw the next punch, landing it on Josh's nose. While Josh reeled from the well placed blow, Castle took advantage of Josh's vertigo and seized a hold of his collar. Breathing heavy, ragged breaths Castle used his free hand to throw another punch into Josh's face, then another and another, "Slutting (punch) is not (punch) a word (punch)," he yelled.

Kate threw herself on Castle, trying to stop the beating. That's when she heard the loud banging of a fist on her door. "Yo, Beckett? It's Esposito, Lanie sent me to get that dress?" Oh thank God! Castle was pulling himself together and holding an unsteady (yet still swearing) Josh at arm's length still clutching him by the collar.

"Cut it out," Castle swore and shook Josh as one of his flailing limbs connected with the side of his head.

"Beckett? Is everything alright?" Esposito called through the door.

"Not really," she admitted as she reefed the door open, allowing Esposito to take in the scene that was her dishevelled lounge room. She watched him quickly absorb what lay before him and cross the space between the door and the two men still struggling on her floor. As expected he gave Castle the benefit of the doubt, probably because he was the only one of the two not trying to hit the other anymore anyway, and roughly pulled Josh to his feet, throwing him onto the couch.

"What the hell?" Esposito demanded.

"Thanks man," Castle obliged, "I was just helping Josh here find the door."

"Yeah...right," Esposito turned to Kate, raising his eyebrows, questioning her.

Before she could offer any better version of an explanation Josh found his voice again, "I told you, I'm not going anywhere." Kate sighed.

"Yeah, right," Esposito scoffed again. He lifted Josh easily from the couch and dragged him from the lounge room, out of her apartment and down the hallway. They could hear Josh's struggle and cursing the whole way to the elevator.