*This idea came to me over Christmas break, and I haven't been able to shake it. I don't want to give too much away, so I apologize if the summary is really vague. I promise you this story is worth a read. I've got some really awesome things in store for this fic, so I hope you stick around. This is set mid-season 4, pretty much right after "Till Death Do Us Part." I don't own Castle. Happy Reading!

(Kate)

Kate Beckett stood outside an old apartment building, tapping her foot impatiently. She needed to get up to the crime scene quickly, but she was waiting on Castle to arrive. Normally, Kate wouldn't hesitate to investigate a scene alone, but lately it didn't feel right for her to go to a murder scene without her partner.

Kate was just about to call Castle and demand his whereabouts when she spied him jogging towards her, coffee and what looked a bag of donuts in hand. He came to a stop in front of her, a broad grin plastered on his face. "Good morning, Detective," he said cheerily.

Kate tried to ignore the way Castle's smile made her heart race, and instead focused on being as annoyed with him as possible. She raised an eyebrow, folding her arms across her chest. "You're late," she said, turning to enter the building.

Castle caught up to her, tugging on her hand to stop her. She turned to him expectantly, praying that her blush wasn't noticeable. He gave her his best puppy-dog eyes, weakening her already shaky resolve. "I'm only late because I know how grumpy you get without your coffee," he explained, handing over the beverage with a smirk. "Besides, it's not like you haven't gone to a crime scene without me before."

Kate rolled her eyes, taking a long sip of coffee to hide her smile. "I know, Castle, but you're so much like a puppy already, I didn't want to run the risk of you getting lost."

Castle clutched his heart dramatically, staggering back a few paces. "Your words," he gasped. "They wound."

Kate couldn't resist another eye roll as she headed toward the elevator. "C'mon, Castle," she called. "Lanie and the guys have been up there for half an hour already."

"The guys?" Castle inquired as they rode the elevator to the sixth floor. "Does that mean what I think it means?"

He looked so adorably excited that Kate had to suppress another smile. "Yes, Castle. Honeymilk's back from his honeymoon." She smirked as Castle choked on his coffee.

"Katherine Beckett," he admonished, once he'd finished sputtering. "I cannot believe that you would stoop to the level of making fun of a treasured friend and respected colleague."

"Oh please, Castle," Kate scoffed. "You're just mad that you didn't think of it first."

Castle pouted slightly as the doors opened. "I did think of it first," he muttered. "You just said it first."

"You can pout later when we don't have a murder to solve," Kate said, making her way through the swarm of cops to apartment 6F. The crime scene was a small, run-down studio apartment. The living area was mostly bare, containing only a shabby futon and a 13 inch tv with rabbit-ears.

Lanie looked up from the kitchenette where she was examining the body of a young man. "Bout time the two of you got here," she remarked. "What took you so long?"

Castle held the bag of donuts out for her to see. "I'm late because I was being a gentleman and fetching you breakfast, Dr. Parish. But if you don't want it…"

"Give that bag to one of my boys, and I won't have to hurt you," Lanie said, smirking as Castle handed the bag of pastries to one of the morgue techs that had come with Lanie.

Kate cleared her throat. "What've we got, Lanie?"

Lanie sighed, turning back to the body. "Caucasian male, one gsw to the head. There's no exit wound, so I'll have to dig for the bullet when I get him back to the morgue. No defensive wounds of any kind, so he either knew his killer or he didn't have time to react."

Kate crouched down next to Lanie. "Do we have an id?"

"Super identified our vic as James Avery, 35," Esposito supplied. "A neighbor called him up here this morning when she noticed a funny smell coming from his apartment. We asked around the floor, and the last anyone saw of Avery was four days ago."

"Liver temp puts time of death around seventy-six to seventy-eight hours ago," Lanie chimed in. "So between one and three Friday morning."

Kate nodded, standing back up. "Espo, I noticed a security camera in the hall. Go over the footage with Ryan; see if Mr. Avery had any visitors around the time of his death. Also, I'd like you to canvass the building. See if anyone saw or heard anything Thursday night into Friday morning, okay?"

Esposito nodded. "Got it, boss." He turned towards the bathroom. "Yo, Ryan, it's canvass time. Let's move, bro."

Ryan poked his head out of the bathroom, excitement written on his face. "You guys are not gonna believe what I just found," he said, beckoning them closer.

Castle lit up immediately. "Oooh, is it drugs?" he guessed. "Nuclear bomb?" He gasped. "Another body?"

Kate silenced him with a look. "What did you find, Ryan?"

"You have to be in here to really appreciate it," the young Detective explained. "But one at a time; this bathroom's really small."

Kate squeezed into the bathroom with Ryan, her jaw dropping immediately. "Oh my God," she gasped, taking in the arsenal of firearms that lined the bathroom walls. "Who is this guy?"

"That's not all," Ryan said, climbing onto the toilet. "There's a loose tile in the ceiling here," he said, pushing it up and sliding it over. "I'm guessing Avery's got more stashed up here, but I haven't gotten around to checking it. I'm thinking the killer might have known about the stash, too. The tile was dislodged when we got here."

"Nice work, Detective," Kate said with a grin. "Before we investigate the contents of the ceiling, let's get photos of all these guns and send them to ballistics. Maybe one of these is our murder weapon."

Ryan nodded absently, focusing on a low corner. "Wait a sec, Beckett, look at this."

Kate peered over his shoulder. "There's a gun missing," she said, disappointment coloring her words.

Ryan sighed. "Yeah. I don't think we're gonna find our murder weapon in here after all."

"That would've been too easy," Kate remarked. "Nonetheless, I want these sent to ballistics for testing. Maybe they'll help us determine why someone wanted Avery dead."

Kate stepped out of the bathroom to allow the CSUs space to work. Castle was at her side immediately. "So, what did you find?" he asked breathlessly.

She raised an eyebrow. "Guns, Castle. The walls were lined with guns. There was one empty spot, so we're guessing the killer took the murder weapon with him."

"Hmm…" Castle started to pace, and Kate could tell he was coming up with one of his crazy theories. "What if he didn't?" he asked, raising an eyebrow at her.

"What do you mean?" she asked, frowning.

"What if the killer used one of Avery's guns to kill him, but then put it back in the bathroom and stole a different gun just to throw us off?" Castle mused, his voice low and excited.

Kate shook her head, fighting back a smile. "And why would he do that, Castle?"

"Maybe he figured that the police would jump to the exact conclusion that you jumped to. Just hear me out," he begged. "He's just killed Avery with a gun from the bathroom. He realizes that he can't put the gun back because the police will test every gun in that room. But he can't take it with him either, because he can't run the risk of being tied back to this shooting. So, he replaces the gun he used and steals a different one, figuring that the police will think he took the murder weapon with him and ignore the gun collection in the bathroom, where the actual murder weapon resides." Castle grinned triumphantly at his logic, which, unfortunately, made a little sense.

Kate resorted to rolling her eyes at him, refusing to acknowledge that he could be right. "Either way, we'll find the gun, Castle," she retorted. "Besides," she continued, trying to distract him, "we found Avery's secret hiding place. There was a loose ceiling tile above the toilet. We wanted to get the guns out of the bathroom before we started digging around up there."

They waited in silence, watching the CSUs carry out weapon after weapon from Avery's bathroom arsenal. After about twenty minutes had passed, during which time Lanie and her team headed back to the morgue with the body, a CSU holding a box full of firearms approached them. "Bathroom's all yours, Detective Beckett," he said. "We'll try to run all of these as quickly as possible, but you saw for yourself how many guns were in there. It could take a couple of days."

Kate nodded. "Take whatever time you need to do your job thoroughly," she advised. She pulled on a pair of latex gloves and started for the bathroom. "C'mon, Castle."

Castle followed her into the bathroom, watching expectantly as she stood on the toilet and removed the ceiling tile. "How can I help?" he asked.

Kate looked down at him, smirking. "You can hold the box," she said, nodding to the evidence box on the floor.

"That's it?" Castle asked, pouting. "Hold the box?"

"There's not really room for you to do much else, Castle," Kate explained. She handed him the loose tile. "Ryan said that the tile was out of place when he got here. It's possible the killer was looking for something. We might be able to pull prints from it."

The ceiling was low enough that Kate could stand on her tiptoes and see into the space. She dug out her flashlight and shined it into the ceiling. "What's up there?" Castle inquired from below.

"Not a lot," Kate responded, assessing the contents of the ceiling. "Just some money and what looks like a journal." She dropped down from the ceiling, bringing the contents with her.

Castle whistled. "That's a lot of money."

Kate shook her head, frowning. "There's got to be fifty thousand dollars here, Castle." She shrugged. "Maybe our guy didn't know anything was up there."

"What's in the book?" Castle asked as she bagged the money.

Kate shrugged, flipping through the small, leather bound book. "Just a bunch of names, dates, and random numbers." She reached the end of the writing, and something caught her eye. "Hmm…"

Castle was immediately behind her, peering over her shoulder. "What is it?"

Kate ran her finger along a jagged strip of paper. "Someone tore a page out here. Probably the last entry." She closed the book, studying it for a moment. "Once we get back to the precinct, let's run these names. They might be our best clue as to who the hell Avery was."

Castle was surprisingly silent as he trailed Kate out of the apartment and into the elevator. When they got off in the lobby, he finally spoke. "I was just thinking, what if Avery was a hit man?"

Kate stared at him in disbelief. "Seriously, Castle? A hit man?"

"What?" he protested. "It makes sense, Beckett; the arsenal in his bathroom, large amounts of cash hidden in his ceiling, and a mysterious book full of seemingly random names. Or are they random? Perhaps they all share one major connection; they're all Avery's victims."

Kate rolled her eyes, exiting the building. "It's a great story, Castle, but let's not jump to conclusions, okay? We still have to solve the murder."

Castle got in the passenger's side of Kate's car eagerly. "Then what are we waiting for?"

Castle sighed deeply, resting his chin on his hand. "This is boring," he complained. "Why can't we run the names from the book now?"

Kate pinched the bridge of her nose, sighing. "Because, Castle, we have to fill out the paperwork before we start playing around with the evidence."

"I bet Ryan and Esposito are having fun on their canvass," he griped. "Why do I never get to go with them?"

Kate looked at him incredulously. "Because you're my partner, Castle. You decided to shadow me. Plus the guys don't want to put up with you for that long," she added, smirking.

"Again with the hurtful words," Castle said, shaking his head. "You're really on a roll today, Detective."

Kate had barely finished her paperwork when Ryan and Esposito returned from their canvass. "You guys get anything?"

Esposito shook his head. "Nada. Most of the tenants we talked to had no idea who Avery was. Those who did, said he kept to himself. And not one of them remembered seeing or hearing anything strange Thursday night or Friday morning."

Kate grimaced. "Did you get the footage from the security camera?"

Ryan sighed, shaking his head. "Nope."

"The camera was a fake?" Castle asked.

"Oh, no, it was real enough," Esposito replied.

Kate frowned. "Then what's the problem?"

"Someone stole the tape that contained the footage we needed," Ryan admitted. "Only the tape we needed. You two find anything?" he asked hopefully.

Kate closed the file and retrieved the journal from the evidence box. "We're about to find out," she said, holding it up. "There's exactly thirty names in here. Let's take ten names each and run them; see what they can tell us about Avery."

They divided the names amongst themselves and set to work. For a few minutes, the only sound came from the clicking of mice and the tapping of keys. There were a couple moments of silence while they waited for the first results and then all four sucked in shocked gasps.

"Yo, Beckett, we got a problem," Esposito said. "Mark Haley, the name I just ran, he's been dead for four years."

"My first guy's dead, too," Ryan confirmed. "Andrew Cross was shot to death in 2009."

Kate sighed. "Tess Whitmore, shot and killed in 2004...case is still classified as unsolved."

"This can't just be a coincidence," Castle said. "Can it?"

"It's a possibility," Kate started. "A very slim possibility, but a possibility nonetheless. Ryan, Espo, what are the exact dates of death for your guys?"

"October 15, 2007," Esposito replied.

"April 4, 2009."

Kate checked them against the dates in the book. "Damn," she muttered. "They match. So does the date for Tess."

"What does this mean?" Castle asked.

Kate sighed. "We'll have to run all of the names to be sure, but it's possible that your hit man theory wasn't as far off the mark as I thought."

Castle grimaced. "I really hate being right about stuff like this."

Kate, Ryan, and Esposito all looked at Castle incredulously. "No you don't," Ryan said.

Castle opened his mouth, presumably to protest, when they were interrupted by Ryan's phone. His joking tone turned more serious as he answered the call. "Ryan…Uh huh…Yeah…Okay…Uh huh...Right..." He gestured for a pen and paper, which Kate handed over immediately. He jotted several things down in silence, only speaking again to end the conversation. "Alright…Thank you."

"What was that about?" Esposito asked, as soon as Ryan had hung up.

Ryan grimaced. "That was ballistics," he started. "They've gotten hits on all of the guns that they've run so far. They're getting hits on cases from as far back as 2004. Every single one of these cases have gone unsolved. I got a list of the victims' names to check against Avery's book, and they're faxing over the ballistics reports now."

He handed the list to Kate, heading for the fax machine as she flipped through the book to check the names. "They're all in here," she confirmed. She wandered to the Murder Board and started jotting down the names of Avery's presumed victims. She leaned against her desk, narrowing her eyes at the board.

"What's wrong?" Castle asked, joining her.

Kate shook her head. "I don't know," she admitted. "Something just seems…off."

"Like what?" Esposito came to stare at the board as well, standing to Kate's left.

"Well, for one," she started, "if Avery killed all of these people, how is it that the cases never connected until now?"

"Because Avery never used the same gun twice," Ryan said, approaching with a stack of papers. "Twelve different guns, twelve different murders."

"Wow," Castle murmured, sounding impressed. "This guy was smart."

Kate raised an eyebrow at him. "Yeah... Smart enough to keep an arsenal in his bathroom, in plain sight." She turned back to the Murder Board, frowning again. "And why keep the guns in the bathroom? Why wouldn't he try to hide them somewhere?"

Esposito snorted. "Where? Our break room is bigger than his entire apartment." He shrugged. "Maybe he figured it was the safest place for them in case a cop showed up. A firearms collection like that, registered or not, would definitely raise suspicion."

"Which is probably why he didn't entertain," Castle mused. "That would be a hard one to explain to a date or to Grandma."

"Something else is off here," Kate muttered. She let her eyes wander over the evidence they had collected, finally focusing on the missing page from Avery's book. "Guys, why would this page be ripped out?"

"Dunno," Ryan replied, shrugging. "Maybe Avery needed to write something down."

Kate shook her head. "It was hidden in the ceiling in his bathroom. Why go to all that trouble just for a grocery list or a phone message?"

Esposito sighed. "You're right, it doesn't make sense, but that still doesn't explain the torn out page."

"My guess is that Avery's killer knew exactly what he was looking for," Kate said. "And either he knew exactly where Avery kept that book, or he got it out of him before he killed him."

"But why leave all that money up there?" Ryan asked. "And why just take one page; why not take the entire book?"

"Well, if our killer knew what he was looking for, he probably knew what Avery was," Castle supplied. "He most likely didn't want to run the risk of being caught with the book and the money. That would make it harder to put the blame on Avery, especially since he just killed Avery in cold blood."

"Whatever was on that page must have been pretty important if Avery was killed for it," Kate said.

"Well," Esposito piped up. "We know that the book is a record of Avery's hits, right?" They all nodded in agreement. "Maybe that page had the name of his latest target…or his next."

"There's a way we can find out, right?" Castle asked, his voice tinged with excitement. "Can we do a rubbing of the next page; see if there's an indentation…" He grabbed the book, but Kate snatched it from his hand and sat down at her desk.

"Hey!" he protested.

Kate raised an eyebrow at him. "Which one of us is the cop, Castle?"

He pouted. "You."

"Exactly," she said. "Which is why I'm going to handle the evidence." She let him pout for a minute before adding, "You can watch if you want, though."

Almost instantaneously Castle was hovering over Kate, taking up way too much of her personal space and driving her to distraction. She looked over her shoulder at him to tell him to back off and was momentarily caught off-guard by his proximity. She swallowed hard, trying to refocus her thoughts. "Castle…"

"Right," he said, clearing his throat. "Personal space." Castle cleared his throat again, backing away from Kate. "I'm going to get some coffee…you want some?"

"That'd be great, Castle, thanks." She watched him make his way to the break room with a fond smile. She turned back to her desk, only to find Ryan and Esposito watching her, arms folded and eyebrows raised. "What?"

Esposito arched his eyebrow higher. "Don't try to play innocent, Beckett. What was all that about?" He gestured randomly in her direction.

Kate rolled her eyes, turning to the torn page in Avery's book. "That was nothing, Espo. I think Castle's overactive imagination is rubbing off on you."

"Nah, that was definitely something," Ryan said, pulling her attention away from the book again. "We all know that if something like that had happened even a year ago, you would've thumped him on the nose or twisted his ear."

Kate swiveled her chair to stare directly at the pair, who were both grinning like idiots. "Alright, Frank and Joe, I think it's time the two of you went back to Bayport."

Esposito frowned in confusion, but Ryan's jaw dropped. "You did not just call us the Hardy Boys," he demanded. "You didn't…"

Kate rolled her eyes again, turning her attention back to the book. "I believe I just did," she remarked offhandedly, picking up a pencil to begin her work. As she rubbed, a name started to emerge on the page, and dread quickly overwhelmed all of Kate's previous emotions.

She could faintly hear Castle's approaching footsteps and Ryan's indignant voice. "Castle, would you compare us to the Hardy Boys?"

"Yes," Castle replied simply, breaking Kate out of her thoughts as he set her mug on her desk. "So, who's the lucky bastard that Avery never got around to killing?"

Kate looked up at him, hand trembling as she handed him the book. "It's you, Castle."

*Whoo cliffhanger! Don't you just love 'em? Yeah, me neither. But don't fret, I won't keep you waiting too long (I hope). Both the title of the fic and all of the chapter titles will be taken from the song "Brighter than the Sun" by Colbie Caillat. Don't let that fool you, though. This story is going to be intense, to say the least. Let me know what you think!