AN: This is only my second crossover story. I hope it makes some sense.

Jamie was at work when Renzouli came up to him, "Hey, Reagan! Wait up."

Jamie turns and looks at him, "Yeah, Sarge?"

"Do you think Jenko would mind you being reassigned for something different to learn from?"

"I doubt she would mind."

"Alright then. Today you will be working with BDU or our negotiators for the day." Renzouli pats Jamie on the shoulder and gives him the assignment paper before walking off. Eddie then walks through the doors.

"Hey what's that?" Eddie gestures at the paper. Jamie looks at her, "Well, Sarge just told me that I am being reassigned to the BDU hostage negotiators. So it looks like you will be partnered with someone else today." Eddie looks confused, "But, why only you and not both of us?" Jamie shrugs, "Sarge thinks it will be a good learning opportunity."

Eddie tries to look unaffected, "Well, maybe I will be allowed to drive now that I'm partnered with someone else." Jamie smiles and laughs, "I'll miss you too, Jenko." Jamie leaves and heads over to his new post for the day.

"Captain Peterson?" Peterson turns around, "Yeah?"

"I'm Officer Jamie Reagan, I was assigned to your task force today by my sergeant." Jamie hands his papers over to him. Peterson looks it over, "It looks like it." He pauses, "Reagan as in Frank Reagan's kid?" Jamie nods. Peterson nods his head, "Let's hope today goes well for us then." For the next few hours Peterson has one of his people showing Jamie around and telling him what they normally do when a call came in.

Meanwhile in the 12 precinct Beckett and the boys are doing paperwork when Beckett gets a call from Castle, "Tell me you need me." Beckett pauses and wonders what exactly he was asking, "What?" She asks ignoring the slightly hopeful tone her voice held. Castle didn't hear it as he was really bored. He explains where he was and asked if there was a murder he could be solving, Beckett is telling him that she is just doing paperwork which is not what Castle wants. He is complaining when he notices the two people in scrubs, "I think this bank is about to be robbed." Beckett doesn't really believe him until she hears over the phone, "Everyone get on the floor! On the floor!"

"Not my imagination! Not in my imagination!" Castle heads back to his mother and hides behind a desk, while Beckett tells Ryan and Esposito to call it in, they are confused until they learn that Castle is at the bank and they start moving in a hurry. Beckett asks Castle to describe what he sees and when he does they are caught by the fourth man, he takes the phone from Castle. "Sorry, your friend can't talk right now." He is about to hang up when he hears Beckett talking, "I wouldn't worry about him, I'd worry about yourself. I've got squad cars on their way." The robber is annoyed, "You a cop?" He looks at Castle, "You called a cop?" Castle stutters, "No we were already on the phone when you guys came in."

The robber is about to say something when Beckett starts talking, "Listen to me, So far, nobody has been hurt and nothing has been stolen. So, if you just leave the same way that you came in, you can just disappear." The robber raises his eyebrows, "You gonna promise not to come look for me?"

Beckett talks softly, but dangerously, "I don't look. I hunt. And trust me, you don't want that. So leave now and this'll just be a quirky little article in the Metro section." the robber looks surprised and impressed by the threat and thinks for a moment before deciding, "Sorry, sweetheart. I'd rather make the front page." He then takes the phone and stomps on it. Beckett clenches her jaw before looking at Ryan and Esposito, "Let's go."

The call comes in and Peterson looks over at Jamie, "Well, looks like you will get some real experience today. Call just came in and there is a hostage situation at a bank, let's move!" Everyone starts to move and Jamie follows Peterson into the SWAT van. Jamie is sitting in one of the chairs finding information that Peterson wants when a woman comes in, he raises an eyebrow, but doesn't think that it is his place, so he keeps an ear out, while still looking for the information.

When Beckett and the boys get to the scene they find that SWAT has taken over already, "I'll go talk to the person in charge, you guys see what you can find out." She heads over to the truck and heads inside. She hears someone demanding information and guesses that he is the guy in charge. The guy notices her, "Who are you?"

"Detective Beckett, Homicide." Jamie and Peterson raise eyebrows over that. Jamie is confused as to what is happening because there hasn't been a homicide and he for sure thought his brother would want to get involved if there was.

Peterson shrugs it off, "I'll be sure to call if someone dies. Meanwhile, I need you to step outside…" Beckett cuts him off, shaking her head, "No, sir. My partner is in that bank." Peterson stops for a second while Jamie turns serious and is about to talk when Peterson interrupts him, "Wait, we got a cop in there?" He is incredulous, Jamie looks at the woman and notices a slight hesitation, "He's a civilian investigator. He and I were on the phone when they took over the bank. He said that there's four suspects in there, they're dressed in doctors' scrubs." Jamie is confused on the civilian part, thinking that his brother would never be able to do that and he was wondering who it was, when Peterson continued the conversation.

"Anything else you can tell me?" Thinking that it was a good observation from the civilian investigators. Beckett nods, "Yeah, I spoke with one of the suspects."

"What was the demeanor?"

"Calm, actually. Very calm." Peterson nods before saying, "Thanks for the intel. We'll do everything we can to get your partner out safe." Beckett looks around, "Okay, so what's our next move?" Peterson shakes his head, "Well, your next move is to leave my command post." Beckett is about to protest when the Captain interrupts, "You want to help your partner? Let me do my job." Jamie notices that she doesn't like that before Peterson talks to him, "Get us a line inside, so we can talk to him." Jamie nods and goes about doing that while noticing that Beckett is being kicked out. He smiles a little when he notices that she rolls her eyes at the captain thinking that his brother wouldn't take being kicked out lying down.

Jamie gets the phone number, "Sir, I got the number." Peterson nods and tells him to dial. When Jamie does Peterson takes a headset, even though everyone can hear what is going on, "Hello," the robber says casually. Jamie gets a shiver at how calm the robber is being. "Yes, this is Captain Peterson-" The robber interrupts him, "I will only talk to the lady cop, the one with the bedroom voice." Peterson looks exasperated. Jamie raises an eyebrow at how just one conversation with the robber has got Beckett into the van.

Captain Peterson gets Beckett back in and complains about her charming the bank robber who will only talk to the lady cop with the bedroom voice. She raises an eyebrow before Peterson tells her she is in. Beckett is slightly happy about that before realizing what she would have to do, "I don't have any training in hostage negotiations." Peterson tells her to keep calm and don't threaten like her homicide training tells her. Beckett takes offense because she usually keeps calm, but she ignores the comment for now.

They phone the bank again, it is picked up, "Who's this?"

"This is Detective Kate Beckett. I understand that you wanted to speak with me."

"Yeah, I don't like the other guy."

Yeah, me neither." She says with a glance towards the captain, who looks at her. She covers her mike, "You told me to build a report." Jamie laughs a little at the slight dig. The robber smiles slightly at that despite knowing that it was in the handbook. He tells her that she can call him Trapper John.

Castle is looking and gathering information on the inside while trying to calm people down. "I work with the police and my partner is going to get us out." He gets more information while heading towards the bathroom.

Esposito tells Beckett that they can't storm the bank because they have no eyes and if they do try there will be a blood bath.

She talks again with Trapper John and he mentions what he wants and hangs up. Jamie is looking for information when an officer next to him sits up straight, "What the…? You see that?" Jamie looks over and notices the blinking light and he nods. He notices Beckett coming over, she looks at it for a minute, "It's morse code." She grabs a pen and paper and starts writing it down. Jamie is impressed with this guy who knows morse code and is still trying to help the cops when he should be scared witless.

They find out that it is about a safety deposit box. Jamie starts looking at the box, "It doesn't look like much other than the two owners accessing it monthly." Beckett looks at him for a second confused before shaking her head, "I'll get my team to check it out." Jamie looks interested at the team comment, but goes back to watching the feeds.

Ryan and Esposito call Beckett and tell her about the dead woman that they found and the missing key around her neck before Beckett sees Alexis. She heads over to Alexis and tries to calm her down while telling her that she promises to save them. Jamie comes out for a second and sees Beckett trying to comfort a redhead. "Detective, we need you in here." Jamie yells.

Beckett listens as Trapper John talks about the medical issue that they are having. He hangs up and Beckett looks annoyed. Peterson thinks that they should storm the bank, but Beckett is thinking something over. Jamie is looking between them when Beckett says that they have a different choice than storming the bank.

She tells them that they could send in one of their own in place of a medic and get information that they need. Jamie looks around, "Who would we send though?" Peterson glares at Jamie before Beckett says, "Me. I have field training, plus it will probably be better that a woman goes in then compared to a man, who could be seen as dangerous." Jamie catches Peterson nodding along with the idea and agreeing to it.

She goes out to the ambulance and changes into the paramedic form, when she exits she catches Alexis' eye and nods before heading inside. Alexis looked confused before realizing what Beckett is doing and how dangerous it is. She tries to call Ash again, but he doesn't answer.

Castle is sitting next to Sal as the door opens. He sees that it is Beckett and not an actual paramedic and grabs at the opportunity. Beckett notices the hostages gathered around the floor and Castle next to the victim. She breathes out a sigh of relief at both Martha and Castle being safe. The robbers pat her down and once she is clear she heads over to Sal and Castle. They talk quietly for a few seconds while Beckett tries to reassure Castle more than Sal. She grabs Castle's hand and holds it for a few moments before she and Castle get Sal onto the bed. He gives her the note about the C4.

Beckett leaves the bank and heads towards Alexis. "They are okay Alexis." She says as she reads the note, "Oh, God." Alexis gets nervous at that before Beckett forces her to get behind the yellow line, using an officer to help her.

Beckett is back inside the van and lets the captain know the message. Jamie is worried about the message as well, but waits for the captain to tell them what to do, also thinking that Beckett has a lot of faith in the civilian investigator. Beckett gets back on the phone and tries to tell Trapper John that the bus is stuck in traffic. Trapper John gets angry at the delays and decides that he is done talking. He aims his gun around and fires. Beckett stops, "What was that?"

"A warning shot, Kate. The next one's for the kill." He yells as he heads towards Castle. Beckett can hear Martha yelling at Trapper John and Castle getting someone to hold her back. Jamie is also panicked because the robber sounds like he is ready to kill the hostages.

"I'm gonna make pretty red stains out of your boyfriend, Kate. I got my gun to his throat and I'm going to paint a Jackson Pollock with his insides!" Peterson is getting nervous at how the robber is acting, before telling Beckett, "You need to calm him down." Jamie is anxiously waiting to see what happens next.

Beckett ignores that as she moves forward slightly and talks softly and dangerously, "Listen to me, jackass. I do not control traffic, so you're gonna have to give me twenty minutes." Jamie raises an eyebrow as Beckett ignores the captain while also insulting and calling the robber names.

"Now you got one minute, Kate!"

Beckett gets even more furious, "No! I've got twenty. Do you hear me? Twenty. Because if you pull that trigger, I will walk through those doors and personally put a bullet through your skull."

There is a tense pause as everyone holds their breath, waiting for a reply when, "Okay, Kate. You've got twenty more minutes." He hangs up and the Captain takes a breath before saying, "Well, that's one way to negotiate." Jamie smiles and looked slightly awed at Beckett and the threat she gave. 'Even my brother probably couldn't have pulled that off.'

Inside the bank, Trapper John looks at Castle, "Your girlfriend is a hellcat."

"Yeah, well, she's not my girlfriend." Trapper John raises an eyebrow, "She too much woman for you? Because I think that the fact that she threatened to put a bullet in my skull means she is definitely too much woman for you, although she didn't deny the boyfriend comment."

Castle pauses before shaking it off, "Ha. So why are you robbing this bank." He goes into detail about what he found out while Trapper John listens. Trapper John kind of ignores Castle while telling everyone to get on their feet.

Meanwhile in the van Beckett is thinking over her conversation. Peterson is explaining what he is planning on doing when Beckett interrupts, "Why didn't he ask me for something?" The captain and Jamie are confused, "What?"

She stands up, "Sir, he gave me twenty minutes and he didn't ask for anything in return. If he wanted to maintain control, he would've asked for something. I mean, this is all way to easy." Peterson shrugs her off while Jamie is considering what she had to say.

"Take the win, Detective." Peterson wants this over with, hopefully happy and he doesn't want some homicide detective to mess that up by overthinking things.

"No, sir, something is going on. We're just not asking the right questions. I mean, why would he bring C4 to a bank robbery? What does Agnes Fields' murder have to do with any of this?" Jamie nods along, bringing Beckett's attention back to him. She thinks he looks familiar, but she ignores it again. Beckett gets a phone call and asks about Agnes, before the bank explodes and the van shakes.

Beckett is frozen for a second before grabbing her gun and heading towards the door. "Wait!" Beckett turns around, "I don't have time for this, the bank exploded, I am going in to find my partner." Peterson pauses before nodding. Beckett takes the teams and heads inside while Jamie decides to follow. He enters behind the other officers, listening as Beckett starts yelling, "Castle! Castle! Castle!"

They hear a voice, "Beckett?"

Beckett finds the hostages in the safety deposit box, "They're here!" Beckett gets inside and heads straight for Castle, Jamie pauses for a second before heading for the other hostages. Beckett and Castle stare at each other and give smiles. Castle is amazed at the smile that Beckett gives him before Martha interrupts them. Beckett apologizes while cutting their zip ties.

They head out where Peterson finds them and explains what happened to the bad guys. Castle thinks it doesn't add up given how experienced these bad guys were. Peterson doesn't care because he has the body parts to prove that they failed.

Beckett looks at them, "Let's get out of here. You guys have someone very anxious to see you outside." Castle and Martha smile and start heading outside, waiting to help Simone. They get pulled into a hug with Alexis, who looks over their shoulders and thanks Beckett, who just smiles at her. Jamie looks around and spots this, thinking that something was going on there.

Jamie heads over to Captain Peterson, "Well, that was an interesting experience, even though it wasn't you as the negotiator, I feel like I learned something." Peterson nodded, "Good luck to you kid." Jamie nods before heading back to his precinct to finish paperwork and then go to Sunday dinner, boy did he have a story for them.

AN: I will continue the second chapter of 4x07, but if you want to see a specific episode with both Blue Bloods and Castle characters let me know. I might not do them in order. Let me know what you think, I know there wasn't enough Jamie, but he will have family dinner in the next chapter.