A/N: Just a bit of fun that came to me after watched episodes of these two NY set shows. I know the title isn't the right number for a social security number for someone in their thirties but Castle fans will recognise most of them.

Disclaimer : I don't own Castle or Person of Interest only the creators and writers of those shows do. This in my small expression of appreciation for both shows.

Number 413193178

Its morning in the library as John Reese walks in on the familiar sight of Harold Finch working away on a keyboard in front of a bank of monitors.

"Good morning Harold," greets Reese in his distinctive hoarse almost whisper.

"Good morning John," returns Finch pleasantly as he looks up from the monitors and nods towards the cracked glass board standing at the other end of the room. "We have a number."

Reese walks over to the board and studies the headshot of an extremely attractive brown haired woman with hazel eyes who looks to be in her mid-thirties.

"Who is she? A model?"

"Ah, no. She's Detective Katherine Beckett of the NYPD," responds Finch looking back down at his monitors.

"She's a cop?" ask Reese with mild surprise.

"Yes, quite a good one from what I see here. She leads a homicide squad working out of the 12th precinct. Youngest woman in the history of the NYPD to make detective and has the highest clearance and prosecution rate in the city."

"A homicide detective is going to have a lot of enemies. It's going to be difficult to identify the threat," suggests Reese as he walks over to Finch to look at the computer monitors over his shoulder.

"Indeed, in fact, looking at her history, I'm surprised the machine hasn't given us her number before now. Besides your run of the mill murderers she's dealt with serial killers, domestic terrorists, an assassination plot of a foreign official's daughter, drone hijacking and most recently she arrested a Senator set for a Presidential run for murder and corruption," lists Finch, his tone becoming increasingly respectful.

"Well, she should be at work by now. Have Detective Fusco meet me outside the 12th. He might be able to give me some more inside information on Detective Beckett and her squad," requests Reese as he walks out of the library.

"And I'll start looking into her current cases to see if that is the source of the threat," calls Finch to Reese's receding back.

Detective Lionel Fusco is sitting in his cruiser across the road from the entrance of the 12th precinct watching the mix of civilians and uniformed officers coming and going. The sudden opening of the front passenger door and the appearance of Reese in the passenger seat causes him to jump.

"Jeeze! One day you're going to give me a heart attack," protests Fusco.

"Oh we both know a heart attack is the least likely way you'll die Lionel," responds Reese ominously.

"Yeah, hanging around with you that's probably right. So why'd you call me down here," he asks with a nod at the precinct.

"What can you tell me about a Detective Katherine Beckett?"

"Beckett? Oh yeah, she works out of here. Well, her and her crew have a bit of a rep, almost famous. There isn't a case they don't close. Some say she's a bit of an ice queen. Carter and I worked with her a couple of times. She seemed OK, a bit intellectual, likes reading but I saw her take down a suspect once and boy is she a hellcat."

"Is she clean? Any HR connections?"

"No, they're all a bunch of boy scouts in the 12th. Their old captain, Montgomery, he was a bit dirty back in the day but their current one, Gates, she's former IA so that shop is squeaky clean. In fact the 12th was one of the few precincts that had no HR people in it at all."

"Must be nice to work with a bunch of honest cops," says Reese sarcastically with a glance at Fusco.

"Very funny," responds Fusco who then pauses, notices something across the road and indicates with a nod of his head, "That's them now."

From the front doors of the 12th they can see four people rushing down the steps and break off into pairs towards two unmarked cars parked in front of the building.

"That's her partners, Esposito and Ryan, both have been with her for years," informs Fusco indicating to the muscled Latino male and the clean cut white guy in the three piece suit getting into one of the cars.

Reese then studies Detective Beckett, long brown hair, wearing a black turtle neck sweater, tight blue jeans and high heeled boots. Then he looks at the tall, brown haired, well dressed, man getting into the other car with her. He didn't look like a cop, "Who's the civilian?"

"He's another reason she's famous. For the last six years she's been shadowed by that rich mystery writer…ah…Raymond…Rodger….ah no Richard, that's right Richard Castle."

As the two unmarked cars start pulling out and driving down the street Reese indicates to Lionel, "Let's see where they're going," continuing in a surprised tone he asks, "A writer and he goes on investigations with her?"

"Yep, from what I heard they met on a case and he decided he wanted to use her as inspiration for his character….ahh Nikki Heat. Apparently he's friends with the mayor so he had the juice to get embedded with her team."

"I bet she loved that," responds Reese with a smirk.

"Sure, not at first but scuttlebutt is that he's one of the reasons that she's got such a good clearance rate. I saw it when we worked together, he's one of those outside the box thinkers that really knows how to pull together evidence into finding the perp. Comes up with some wild theories sometimes. Now they have much more personal reasons for working together."

Reese glances over a Fusco surprised again and asks, "They're in a relationship?"

"Oh yeah, there'd been rumours for years, hell just look at her. It obviously was not just her detective skills that attracted writer boy. A few months back it was in the paper, they're engaged."

Thinking with regret about the recently departed Joss Carter, Reese says almost to himself, "Must be nice to work with someone you care about."

Even a rough guy like Fusco had picked up on Reese's feelings for his old partner and pauses for a moment before continuing, "Further proof that they're good at putting away scum bags. Normally the department wouldn't let people in a relationship keep working together."

"Probably also helped that he's friends with the mayor and not actually with the NYPD," observes Reese.

They continue following the two unmarked police cars for quite a while down several streets until they both park in front a disreputable looking apartment building. They watch as the occupants of the cars get out, head to their respective trunks, open them and start pulling out and donning bullet resistant vests. Reese grunts with amusement as he sees that instead of the usual POLICE as on the other's vests that Castle's has WRITER emblazoned on it.

Finch's voice in his earwig interrupts their observations, "Are you there Mr Reese?"

"Yes Finch, we've followed Beckett and her team to an apartment building on West 177th Street in Washington Heights."

"Yes, I've gained access to Detective Beckett's active case file. That's the address of the prime suspect for the murder of a college student they're investigating. They have their evidence and are there to arrest him."

Reese watches Beckett and her team gather near the front door for a final brief before entering, "Looks like they're about ready to go in."

The volume of Finch's voice suddenly goes up a notch and he starts speaking rapidly, "Mr Reese! One of my search algorithms found information in a Federal database on that address. While the apartment on the 2nd floor holds Detective Beckett's suspect an apartment on the 4th floor is listed with the DEA as being a suspected drug lab for the Cortez cartel. It's a secret file with information from an undercover agent so it's not information disseminated to other law enforcement agencies."

That gets Reese's attention, "A lab for the Cortez cartel will be heavily guarded. They'll see cops and think they're here for them while Beckett and her team won't know what their walking into."

"The Cortez cartel?" asks Fusco nervously after hearing Reese's response.

"Call for back up Lionel," instructs Reese as he gets out of the car and starts walking across the street to the apartment building.

"What are you going to do?" yells Fusco to him as he departs.

"What I usually do," replies Reese as he walks away and watches Beckett and her team enter the front door of the building. Looking for an alternative way in, he spots the fire escape in the alley down the side of the building and strides over to it. He jumps up, grabs the ladder at the end of the escape and starts climbing.

"I'll contact Miss Shaw," says Finch in his ear.

"No time," responds Reese only slightly breathless as he rapidly ascends the fire escape to the 4th floor. Once there he draws his gun and screws on a silencer so as not to attract the attention of Beckett's team if he has to fire and peers through a window. Seeing only an elderly African American couple sitting on a couch, watching TV. He tries the window, finds it unlocked, opens it and climbs into the apartment.

To the shocked occupants of the apartment he says apologetically, "Excuse me, just passing through," as he quickly moves to the front door.

Once there he pauses as he hears the sounds of shouts and pounding feet outside the door. He opens the door slightly and through the crack spots several Hispanic male gang members carrying an assortment of pistols and automatic weapons down the hall to an exit sign indicating an internal stairwell. Just as the last gang member passes the doorway Reese opens the door, grabs him by the collar, pulls him off his feet into the apartment, dumps him on the floor and with the hand holding his gun, hits him hard in the face, knocking him out with one blow.

One down, Reese moves quickly but stealthily after the rest of the gang members as they disappear into the stairwell. He catches one more just before he enters the stairwell and knocks him out by pistol whipping him in the back of the head. Inside the stairwell he moves rapidly and catches the next one and after a quick flurry of blows the criminal is down. Continuing down the stairs he catches the next one on a landing and again engages in hand to hand combat. This time the next gang member, half way down the next flight of stairs notices the fight behind him and moves to intervene. Getting the upper hand in his current fight and seeing the other approaching Reese strikes his opponent with some decisive blows and as he reels away grabs him and throws him into the approaching gang member. Both go flying and rolling down the stairs.

As he strides down the stairs and passes the two gang members groaning on the landing he fires two quick shots, one into each of their legs. Five down and he is continuing to move fast down the stairs. The next two gang members also now know that something is happening behind them. They stop on the next flight of stairs and at the sight of Reese they raise their weapons. Before they can fire there are the sounds of two quick silenced shots as Reese fires first. Both go down with bullets in their legs.

Seven down and Reese can see that they are almost at the second floor. At the last landing he encounters two more of the gang and rushes them before they can get their weapons up. His gun goes flying and he is forced to engage in a desperate brawl with the two opponents. It takes a good five seconds for him to take care of these two but they are both soon sprawled on the landing unconscious. Reese looks down the stairs and sees those five seconds have given the last gang member enough time to get to the second floor. He is standing in the doorway aiming his gun at the back of Detective Beckett who Reese can see is standing at what must be the doorway of her suspect and has no idea she is about to be shot.

Before Reese can move, either towards his gun or the criminal there is a shout, "Kate! Lookout!" and the gang member goes flying as Castle appears, tackling him. They start struggling on the landing with Castle getting punched in the head a few times. Reese moves to assist but after an exchange of blows Castle has the criminal on his back and is delivering punch after punch to his face, incapacitating him.

Nodding his head and smiling in surprise and approval of Castle's efforts and seeing that there are no more threats Reese quietly picks up his weapon and makes his way back the way he came.

Castle is sitting on the back bumper of an EMS bus, holding an ice pack to his throbbing jaw. He looks over at Beckett who is talking to a short, thickest detective and hears her say, "Thanks for calling the cavalry Detective Fusco."

"No problem, Beckett. I'm just glad I was in the neighbourhood," he hears the detective reply.

With a nod Beckett takes her leave and walks over to where Castle is sitting in some discomfort. She smiles that special smile she only has for him when she sees him watching. Upon reaching him she affectionately brushes back the hair from his brow and asks with tenderness, "You OK Babe?"

"Yeah, it only hurts when I talk," replies Castle in the tone of a sulking child.

"Oh well that's a plus then," she returns with a smirk trying to lighten his mood.

"Ha Ha! Where did those guys come from?"

"Looks like there's a drug lab on the 4th floor and they thought we were here for them. Weird thing is there were ten of them including the guy you beat to a pulp," she smiles at the memory of him flying to her defence, "the other nine guys were all incapacitated before they got to us between the 4th and 2nd floors. Some were knocked out and some had been shot in the leg."

"Shot in the leg?"

"Yeah, very skilfully, enough to stop them but not to kill….,"she pauses, her memory triggered, "Wait, I think I remember about some reports of a guy in a suit wanted for taking out criminals and his MO was shooting them in the legs."

"Hey, when I was fighting that gang banger I think I saw a tall guy in a black suit standing on the landing above us," exclaims Castle.

"Hmm, I'll get Ryan to dig up those reports when we get back to the precinct. There's something going on here," she muses.

They share a silence as Beckett continues to ruffle his hair.

"That's fifteen times now that I've saved your life," says Castle with a return of his sulking child voice.

Beckett leans forward and brings her hand down from his hair to cup his cheek. Looking directly into his blue eyes and in her most seductive voice says, "Well, I'll just have to show you how grateful I am when we get home tonight."

From a block away Reese watches the detective and the writer share a smile. He turns, starts walking away and taps his earwig, "I think we're done here Finch."

"Indeed Mr Reese, we have another number."