Author's Note - So this little crossover came to me as I was watching Castle and looked at the actor who plays Detective Ryan and he really reminded me of Brian Mahoney, like they could be related. That got my wheels turning for this story, using my existing BDS fictions, with Quinn and Duffy (Quiffy, I love you DeDe) and working in some Castle, because how do you not love Nathan Fillion? So it's just a one shot that has been in the works for a while finally got it down.

Legal stuff - I do not own any characters associated with Castle or The Boondock Saints or The Boondock Saints II: All Saints Day.

Shout outs (this is my favorite part): A huge thank you to DeDe324 and Rhanon Brodie for looking this over in its infancy and helping me get it to where it is now. You gurls are the bestest ever! Love you to pieces!

So I hope you all enjoy what I have pieced together, read and review, love to know what you think. Thank you!

"Hey Castle," Esposito called and the writer looked up from his coffee, "you like weird stuff," he tossed him the newspaper, "the 26th precinct caught this last night. Pretty freaky, pennies on the eyes, vics are real bad guys and as of now the feds that took over have no suspects." Javier's voice turned up at the end, he knew what he was doing; egging Castle on about the Saints, always a few cases that made their way into the papers and he lit up like a Christmas tree. Kevin Ryan cringed a bit when the pennies were brought up then glared at his partner and shook his head, just waiting for the inescapable…

"Ryan is your cousin busy," Castle asked for what seemed the 500th time, "Do you think I could talk to him?"

The Irish detective sighed slightly looking at Javi and Kate as they suppressed laughter and 'found' other things to do. Kevin looked at Rick and gave him the answer he always gave him, "I'll call him, and see what he says." The look of pure boyish glee that washed over Castle's face every time Detective Duffy was called was priceless. Javier, Kate and Kevin all had pictures of it on their phones. Castle shoved his nose in the paper studying the paper, the crime scene photos, and the reporter's story. Ryan sighed and dialed Duffy's number, "Hey Quinn, Duffy around? Hahaha, yeah Castle again, no still doesn't know about you. Yeah, thanks cuz." He waited for the usual 'no, never gonna happen Kev'. "Hey Bren, how are the kids? Jenny's great, yeah, hey so there's been another Saints, yeah, the writer's asking about you again. Wants to know if you'll….what? You'll come...must be snowing in Arizona. Yeah, yeah bring Quinn and the kids we'd love to have you if you survive Castle. I'm telling you Bren he's a major Saints fanboy. Awesome, I'll see you soon." Kevin hung up, sighed one more time preparing for the writer's reaction. "Well Castle, you're getting your wish, my cousin will be here in a day or two."

A huge grin plastered over Rick's face as he looked up from the paper, he hugged Ryan, "Thank you," he whispered then left. Castle got home overjoyed and giddy he enthusiastically hugged his daughter Alexis and his mother, Martha while crushing the paper in his hands. He looked at the two red heads, "I need my box." He went off to his office and started digging for it handing the paper to Alexis.

Alexis and Martha shared a confused look with each other, then looked at the headline and then stared at the open door of the office, "Oh, no," they said in unison.

Javier nudged Detective Kevin Ryan at the sight of the pretty ginger that got off the elevator, "Who's the red head," he asked taking in her figure.

Ryan looked up and smiled instantly recognizing the dark red hair, "Hey Quinn," he called. He playfully nudged his partner, "That's my cousin-in-law, eyes off man," he laughed as he met Quinn hugging her, "You look great as always, where's that no good cousin of mine?"

"Should be up soon," she smiled at the Irish cop, looking around him at the Cuban throwing him a smirk, "He's corralling Rosie and Colin, you know how they are, love anything to do with their dad's profession."

The elevator bell rang out and the doors opened and spilling the red head's husband and two children causing a ruckus. Quinn and Kevin laughed as Colin and Rosie charged over the New York detective talking over each other asking questions.

"Hey, one at a time," he looked at his cousins, "Catch you two later," he grabbed the kids and took them to the evidence locker. "Hey Javi, show 'em around and introduce them to everyone."

"Hey gorgeous," Duffy sidled himself up behind his wife, moving her hair from her neck kissing her jawline. The red head sighed contentedly into her husband.

It had been a quiet and peaceful five years since Connor and Murphy had left for Ireland. Nothing out of the ordinary had happened, they hadn't heard from them and the Duffy family had gained a rambunctious 3 year old in Colin. Life was good. There were offers for Quinn's story, book deals, movie deals, TV series, while tempting she turned them all down. The ginger had been through enough and so had Connor and Murphy.

The Cuban detective made his way to the couple outstretching his hand, "Javier Esposito," he took Quinn's hand then Brendan's.

"Detective Brendan Duffy and this is my wife Quinn. You're Kevin's partner?"

"Yep, follow me, I'll introduce you to the rest of the team," he flashed a charming smile at the red head. Esposito turned as Quinn looked at Brendan suppressing a giggle. They walked up to a stunning brunette and a ruggedly handsome man who didn't fit the detective profile and looked oddly familiar. "This is Detective Kate Beckett and this is Richard Castle."

"The mystery writer," Quinn said.

The left side of Castle's mouth pulled up into a charming half smile, "You've heard of me," he moved forward taking her hand kissing it lightly. Kate elbowed him as she rolled her eyes.

"Yes, Mr. Castle, I'm a fan. Loved Derek Storm, made Duffy here dress up as him once for Halloween."

"Detective Brendan Duffy," the name caught his ear, the Boston cop nodded. "The Detective Duffy that was assigned to the Saints of South Boston case," Duffy nodded again. The writer's mouth dropped a bit. Castle turned to the pretty red head and his eyes got wide; he recognized her, she was older but Quinn still had that youthful appearance from her newspaper pictures in 1999 and 2008, "You're Quinn Cavanaugh," he said almost a whisper and he was in sheer awe, never had he been so close to anyone who had known the Irish twins. "You knew them."

"Mr. Castle, we both knew them, but it's been years since we've heard from them." Castle opened his mouth to speak but Quinn cut him off, "We plan to keep it that way."

"Why, the Saints are a great story," Rick argued, almost whining, "I'd love to write a true crime story," he was beaming, like a kid in a candy store.

Duffy pulled Quinn into him, "A great story on paper, not so much in practice," she pulled down the V-neck on her shirt further to show the scar she received the last time the Irish twins came visiting. "They leave their marks in very permanent ways."

Ryan looked his family both blood and work related, knowing that this wasn't how he wanted them to meet. The Saints, they always came up. Connor and Murphy were like ghosts, they haunted his cousin, who was almost like a brother. And Quinn, that poor girl had been through more than a body should ever endure. Once Castle found out that he had known someone that had worked on the case he begged the Irish detective to bring them to New York. Ryan finally gave in, but prepped Quinn for the inevitable offer from Castle. He looked at his two little cousins, finally calm after being given handcuffs, Kevin knew Brendan and Quinn wouldn't let the boys come back into their lives and he wouldn't either.

The detectives and the writer looked shocked at the deep scar marring the alabaster skin of Quinn's chest. It was like a cone of silence had been placed around the five of them, no one said a word. They all stared at the unassuming red head.

Duffy broke the silence, "You see Mr. Castle she's been through enough." The Boston detective's green eyes meeting Rick's blue eyes silently pleading with him to give up. Quinn hadn't heard any news from or of Connor, Murphy or Romeo since that night on the docks, but Duffy, Dolly and Agent Bloom were in regular contact, especially after they found out Smecker was still alive.

"Come on Castle leave the story alone," Kate prodded, giving a nod to Duffy then a look of respect to Quinn, the head female detective of the 12th precinct shared almost the same scar. Kate knew it took guts to show it to strangers and turn down an offer from Castle. Beckett placed a hand on her scar and nodded to Quinn and the red head knew, mouthing 'thank you' the brunette cop nodded and yelled, "Hey Ryan, take the day and enjoy time with your family," she called. Duffy and Quinn collected Colin and Rosie who were handcuffed together and giggling hysterically while running away from Cousin Kevin. Once the handcuffs were removed the family and the New York detective left. Leaving behind a stunned Beckett, Esposito and Castle, who looked at one another almost dumbfounded; Kate sighed, "Let's get back to work," she said, nudging the writer, "You ok Castle?"

"Why'd you let them go," he complained.

"Didn't you see where her scar was? Look familiar to you," Kate touched her chest.

A wash of revelation came over Rick and he sighed pouting a bit, "Yeah, it just would have made a great story."

Duffy waited until everyone was asleep to sneak out to call Smecker, he lit a cigarette. He had quit but still lit up when nervous, "Hey, we might have a problem, I need to talk to them….No it needs to be tonight. Yeah I can be there soon."

The Bostonian drove for about 20 minutes to the warehouse Smecker told him to go to. The boys were already there, no weapons to be found, but never without a shot or a cigarette. It was good to see them after the last escapade; it was a bitch to clean up. They got up and embraced Duffy.

"How's Quinn," Connor asked.

"Good, really good," he replied hugging Murphy as Smecker entered with Bloom.

"Wha's this abou'," Murphy asked.

Duffy sighed as he looked at Smecker and Bloom then back to the boys, "There is this writer," as soon as the word 'writer' made it out of his mouth the twins threw their hands up and started muttering profanities, 'no fuckin' way, outta your fuckin' mind, gotta be shittin' me'.

"Listen boys, I think Duffy's got something here. This writer, Castle, wanted to write Quinn's story, but if he writes your story," Smecker paused letting the realization sink it, "It keeps her out of it, and helps your cause."

Duffy nodded, "Plus he loves you guys, a huge Saints supporter. He won't write a bad thing about you. This is a golden opportunity for you to clear your name and tell the public what you're really doing instead of letting them guess."

"Absolutely," the Southern drawl of Bloom entered the conversation, "Think of what this publicity could get you."

"We don' wan' fame," Connor spat out.

"We ain't talkin' fame darlin'," she told him, "I'm talkin' about clearin' the good name of the Saints. You two have it split down the middle, teetering on either side of the public persona of good and evil. With this writer, that would push it back into where we need it to be."

"Exactly," Duffy added. "He could help you, just give him a chance and if you don't like what he does you can walk away. You two are the ones holding all the cards." The MacManus boys looked at each other and shook their heads. Duffy's face dropped, "If you're not gonna do it for me or your reputation, can you at least think about it for Quinn? Once people find out she dated you Connor or that she knew you both or was witness to what you did they hound her for details. Castle seems like a stand-up guy, but do you know how many restraining orders I've had to get because people won't leave her alone," he said frustrated.

Connor and Murphy looked at each other again, then to Smecker, Bloom and finally landing on Duffy. Connor and Duffy's eyes met and a silent understanding was met. The boys nodded.

"Quinn stays ou' of et," Connor demanded.

"No question," Duffy said with a sigh of relief.

"Take us ta 'im," Murphy said.

Rick turned the lock on his door, it was one in the morning, and both Alexis and his mother were asleep. Going right to the kitchen and throwing his keys on the counter. He was halfway through the cold Mu Shu when there was a knock on the door. Castle put the Chinese down, wary as he walked to the front door. Looking through the peep hole and saw Duffy. He opened the door cautiously for the Bostonian, Castle tried to talk but he was cut off by the detective.

"You wanted a story Castle, I'm here to give you one, and so are they."

Castle's eyes got wide as Connor and Murphy came into view and once he realized just who he was face to face with he was like a kid on Christmas morning and almost squealed. "Shut it," Murphy silenced his excitement. "We're doin' a favor for 'im," the darker haired twin nodded to the detective. Both men were not happy about talking to Castle; they had been living under the radar still doing the work they were called to do in New York.

"Come in," Rick said as he moved letting them in, "Let's go in my office we'll have more privacy in there." He led the three men into the office and shut the doors.