If Kate Beckett was ever sure of one thing, it was that never in a hundred lifetimes would she ever have expected this. (An AU version of Probable Cause)

A/N: First of all I'd like to thank Lou (InkyCoffee) for being the prompt overlord and randomly tweeting out prompts that inspired this. Prompt is at the bottom of the page. It's super angsty and I'm not sorry. Enjoy!

If Kate Beckett was ever sure of one thing, it was that never in a hundred lifetimes would she ever have expected this.

Of course Richard Castle had been in her interrogation room before. Several times, as it happened, but not like this; never like this. This Richard Castle was a broken man: head bowed with chin to chest, hair mussed from raking his fingers through it so many times, collar of his shirt upturned and wrinkled, wrists shackled together on a chain looped through the table to the floor. This was the Richard Castle she thought she'd never see.

Thinking back a day earlier to when they found the gruesome scene in Tessa Horton's apartment, Kate's stomach churned and she felt nauseous. At the time, when she first saw the body, saw the peculiar ritualistic nature of it all, she had actually thought to herself, "It's a shame Castle isn't here; he'd like this one."

The thought surprised her slightly, because she hadn't thought about the writer in perhaps a week or more; that was a new record since his disappearance from the precinct and her life four months earlier. She had been trying not to think of him every hour of every day like she had for the prior one hundred and twenty-some days; she had been trying to move on, but after four years that was much easier said than done.

Four months earlier, after a bizarre case involving what appeared to be the undead, Castle had told her that case would be his last; he was ready to move on from shadowing her. To say that she had been stunned would have been an understatement. Shocked, horrified, angry, clawed-in-two seemed among the other descriptors she could use.

He'd been pulling away, she was aware of that, but she honestly thought they could get back to the place they once had been—the place on the path to more. He made the rounds saying goodbye, shook her hand and kissed her cheek like he had at the end of their very first case together, and then simply walked into the elevator and left her stunned and borderline traumatized behind.

All things considered, their parting had not been on poor terms. She might have even gone so far as to say they parted as friends. They had been in contact just a few times since—a random text here and there with limited meaning. He had also stopped by the Twelfth twice, though she missed him both times: once due to a day off, the second time due to being in interrogation.

Still, even after all those days, all that time with Dr. Burke talking about the situation practically ad nauseum, she could barely wrap her mind around his absence, the dissolution of their partnership. And now, to have him back like this…nothing made sense anymore.

Her world fell apart at the touch of a finger—quite literally. The fingerprint on the doorframe at their victim's apartment to be exact.

As with any crime scene, CSU examined every surface of the room in which the victim was found. In this case: the main living area of her own apartment. They checked for prints, DNA samples, hair—everything and anything that could help find witnesses or the killer him or herself. Unfortunately, most times the prints or DNA collected did not yield any matches. If they did, she and her team surely would not have been as busy as they always seemed to be, but it was simply a nature of their job.

The prints on the exterior of Tessa Horton's apartment matched immediately to one Richard Castle. It was an eight point match, so far from the most damning of matches. In fact, a halfway good lawyer (and they knew Castle would have an extremely good lawyer) could probably get a suspect off on such a low-by-standards matching. The fingerprint being on the outside of the door did make it seem almost reasonable. Perhaps Castle had paid Tessa—or her roommate—a visit over the prior week or so, which would certainly not be a crime. Still, being that it was Castle, it seemed odd.

Then, they interviewed Elle, Tessa's roommate, who described their victim's secret boyfriend as rich, handsome and generous—three adjectives that would easily fit the writer. Though, as Ryan was quick to point out, would also fit several hundred other men living in Manhattan. Kate agreed, and they returned to the apartment to search some more.

When the earring found in the couch lead them to the security camera footage from a high-end jewelry boutique Kate was excited; thrilled. Maybe having their victim's mystery man on film would not be as good as having his business card in her hand, but it was most certainly a step in the right direction. And then Kate saw the video.

As she had been hopelessly in love with him, Kate Beckett was incredibly familiar with all things Richard Castle. The way he moved, the way he walked, his mannerisms, and the way he looked from every angle. The man on the video paying over twelve thousand dollars for Tessa's earrings was so eerily identical to the mystery writer that Kate had to excuse herself from the room. For the first time since her rookie year as a cop she was certain a case was going to nauseate her to the point of vomiting.

She knew Castle was the man on the video. She knew it in her bones, but it didn't make sense.

Richard Castle was many, many things—some of them good, some of them not as good, but none of them a murderer. She knew in her heart of hearts that there was no way Castle would kill anyone let alone commit such a gruesome, twisted crime. It simply wasn't possible. From the looks on the faces reflecting back at her, her team felt similarly.

Bank records, more security cameras, and a few tears she tried her best to hide behind a curtain of hair later she found herself outside the door to Castle's loft. They presented him a warrant to search the premise, Ryan and Esposito held him aside, and Kate was certain the look of utter betrayal on his face as she walked past him and he pleaded out her name was one that would be burned into her mind forever. But she pressed on; put on her stoic face and did her job. She was there as her team found the matching bag, the rope inside and the bloody shirt. From that point forward she existed in a state of suspended disbelief.

This just could not be happening.

Yet, it most definitely was.

Straightening her shirt, Kate took a step back from the two-way mirror and prepared herself to enter the next room and interrogate her former partner, best friend and—well, she couldn't think about that right now. Right now Castle was just like any other suspect.

Except he wasn't. And everyone knew that.

Still, she turned, prepared to be as professional as she knew she could, but found her superior blocking her path. Gates gazed at her, her reading glasses held loosely in her left hand, and Kate could feel judgement pouring over her like a wave. She dipped her chin and moved to pass the woman but, as she did so, Gates said, "Don't go easy on him, Detective; I'll be watching." Kate said nothing in response, but moved swiftly from the room.

Kate had barely crested the edge of the threshold when she heard, "Beckett! Thank god!" come from the detained man. He did, indeed, sound like a man praising the heavens above and she couldn't say she was surprised; he had been secluded in Interrogation Room 1 for almost forty minutes by himself. Based on what she knew about him, she was certain he was in complete agony.

She didn't greet him as she normally wouldn't to any suspect seated in that chair. Instead, she entered the room with head held high, shoulders squared, and with a confident stride. She placed the folder of photos and other evidence down on the table before delicately pulling out the metal chair opposite the writer, being mindful so that the feet did not scrape stringently across the floor. Then, with hands clasped before her, she sat and took him in.

Castle's ice blue eyes, usually filed with such joy and jest, expressed his utter terror and confusion. Looking at him, looking at his face, his smile, the little crinkles at the side of his eyes, used to comfort her, but now everything about him stirred a sense of dread within her gut and she fought to keep herself from looking away. She moved her gaze from his eyes to his nose, mouth, cheeks, hair—everything that should have seemed quite normal, but was anything but.

How many nights had she spent dreaming about his lovely, ruggedly handsome face? Before he'd left the precinct the answer probably would have been: almost every. After his absence, it had been most assuredly every. She would dream about him, have dream conversations with him, dream fights with him…dream sex with him on occasion. She would wake up more hurt and confused than before, the gaping hole in her chest—the one from emotions not from a bullet slug—throbbing as she wondered why he had stopped loving her.

Castle telling her that he loved her was perhaps the strangest moment of Kate's life as it added to the barrage of shocked emotions her brain was progressing through while she lie on the grass in a graveyard bleeding out from the sniper's bullet to her heart. She had been stunned, confused, a little angry, but most of all relieved. He loved her. Someone—a wonderful, kind, incredible, miraculous man—loved her. Her—broken and battered, standoffish and sometimes too secluded for her own good. Her.

That moment was the one she clung to as she faded in and out. It was the one she thought about when the pain in her chest seared so deeply she wished for death just so it would end. It was the exact second she thought about for the next several days as she drifted in and out of her pain medication soaked haze. She would wake up whispering his name, praying she had the strength to return his sentiments and cursing herself when she concluded she did not.

If he loved her then—disastrous mess as she was—why didn't he love her months later when their partnership was stronger than ever—when they were closer than ever? What had changed and why?

Dr. Burke told her she was being unfair and he was right. Castle was a human being, just like she, and he was entitled to his own set of feelings, emotions and decisions. Sometimes there wasn't a concrete answer for everything, Dr. Burke had said, sometimes things just were what they were.

Kate Beckett could not accept that, for if she could she would not have been Kate Beckett. She needed to know the reason why—she always needed to know the why. Deep down in her molecular structure, every inch of every cell in her body needed to know why—for everything. Why did people do the things they did? Why had her mother been murdered? What caused people to turn so viciously on one another?

Finding the answer to the question why had been the reason she turned to Castle's books in the first place. They gave an explanation and a reason. They gave her the answers. So why couldn't he give them to her in real life?

There had to be a reason—there was always a reason. Was it something she had said? Something she had done? What flipped the switch? She had spent hours—days—of her life mentally reviewing their conversations and interactions, but she had yet to find a solid conclusion. That was when the more masochistic side of her brain began to speak up.

Maybe the reason was that he'd simply grown sick of her—sick of waiting for her to turn into the person he could be with. Sick of her not being normal—capable of letting go of her fears and having a regular, open, intimate relationship with him.

Dr. Burke had pointed out that perhaps she was expecting too much of Castle. Perhaps he had seemingly given up on something but in reality just took a step back not knowing what there really was to lose. She had not been direct with him. She had implied and danced around the issue—like she always danced around her true feelings. God forbid she tell anyone what was really going on beneath the many layers of the Beckett Onion.

She thought he knew; she thought he understood. Maybe that wasn't enough. Maybe he hadn't really understood, or thought he had but hadn't in the end. Maybe he was confused, uncertain and it had gone on too long without further clarification—nearly nine months since they'd halfway talked about it—and he had merely given up.

That was what she was trying to live with up until the point at which he tumbled back in to her life: this was her fault.

Dr. Burke also wisely pointed out that it was never too late. They hadn't even ended on poor terms. Picking up the phone and calling him would have been all too easy. She could also text and ask him to meet for a drink, for coffee. Then she could explain. She could ask questions. She could get closure.

Having an open, honest conversation? Right. When would that ever be her reality? It wasn't her style, but god, she wanted it to be. She wanted to know—even if it would hurt. Even if it would mean she'd never love again for the knowledge that she and she alone had driven away the one man who would have been her partner for always, her comfort, her one and done was almost too crushing a thought to bear.

She did, at least in theory, plan on having a conversation along those lines. That was to say she wanted to and hoped she'd have the strength when the time came. She was invited to the next Nikki Heat book release party and had every intention of going. She thought maybe they'd get to talking at the party and that would lead to coffee another time. They would take and maybe…maybe…

God, she was a coward when it came to her heart and she hated that, but she had tried with him, she had tried so hard that it left her sobbing in her bed more often than she would ever admit only to have it fall apart in the end.

But that was the way it was, wasn't it? Everything in her life seemed to fall apart eventually. Even this.

"Beckett, please say something. Please tell me you know I didn't do this."

"I know what the evidence says and it isn't good."

With that, she flipped open her file and studied it carefully. The writer continued to plead.

"Kate, I don't know what's going on here—honestly, I've never heard of this girl. Tessa? I don't know her; never met her. Don't even know what she looks like. But, Beckett, I swear to god-"

"Where were you two nights ago?"

He blinked at her, almost started. "Two nights ago?"

"Yes. Let's say…starting at seven all the way to midnight."

"At home—at my home. In the office. Trying to—trying to write." He said the task as though it were an inconvenient but necessary chore like scrubbing a toilet or cleaning up a mess on the floor.

"Can anyone confirm that?"

"Ah, no."

"Your mother? Your daughter?"

"Alexis doesn't live in the loft anymore."

Kate's gaze shot up to him and her stringent interrogator exterior slipped into one of concern until he explained, "She's staying in the dorms. First semester started already."

Oh right. That made sense. Nodding with relief, she asked, "And Martha?"

The writer shook his head. "She was out all night and you know my 'don't ask don't tell' policy."

"No delivery men, neighbors…no one can confirm you were home?" She questioned; he shook his head. Picking up a photo from her file she flipped it around so he could exam it properly and asked, "When did you meet Tessa Horton?"

"I haven't. As I said, I never met her; I don't know her."

"You were never at her apartment?"

"No."

She picked up another page in her file—a photo of the entrance to the crime scene—and flipped it around for him to see. "This is her apartment. Look again. Were you there?"

"No."

"Your fingerprints were."

"Where?"

She shrugged. "Everywhere. The door frame, the door knob, inside…" Okay, that last part was a lie, but she was trying to trip him up, provoke him.

"That's ridiculous I was never—frame. Framed! I'm being framed!" He proclaimed as though he had just solved the clue to the puzzle he'd been agonizing over for a lifetime. "Beckett that's it—the story that makes sense. I'm being frame. Someone got my prints somehow—I don't know how. One of those Mission Impossible like gloves when they shook my hand or something and then they—what's that?"

His voice when from excitable to barely above a whisper the second she put the third photo in front of him. It was a screen grab from the surveillance photo at the jewelry store showing him—or a man who was absolutely his carbon copy—purchasing Tessa's exorbitantly priced earrings. Kate lifted her right hand and tapped her index finger just above the photo. "That's you, isn't it?"

"Where is this from?"

Her tone slightly impatient she asked, "Is this you or not in the photo, Mr. Castle?"

Presumably at her sudden formality, the writer gazed up at her and responded in a clipped tone, "I don't know; where was it taken?"

"The jewelry store where these earrings were purchased," Kate said, adding yet another photo—this one of the discovered earring—to the pile.

"I've never seen those earrings."

Kate picked up another document—a photocopy of the cashier's check used to pay for the item in question. "This is the check you used-"

"I didn't!

"-to purchase these earrings."

"It's a cashier's check, Beckett; there's no evidence I paid for the earrings."

Kate picked up yet another sheet of paper. "This is a statement of your account showing a withdrawal of this exact amount on the same day."

Castle snatched the paper from her grasp as best he could with his restricted hands. "You went through my financials?"

"The evidence-"

"Is wrong." He concluded for her. Castle dropped the sheet of his financial records back to the table before continuing. "Beckett come on. This is all smoke and mirrors—fabricated evidence. You know me. You know who I am. I didn't do this; I couldn't. Beckett. Tell me you know that. Tell me!"

Inside, she was screaming, crying, falling to her knees before him and promising she would fix this for him—for them—but on the outside she refused to register his pleas.

She knew he could never have done this. Barring a video of him actually committing the gruesome act she would still believe in his innocence. Even then, she'd struggle and wonder if he'd been under duress, if his family had been threatened—if there was even the smallest of reasons that could explain his actions. Richard Castle didn't hurt people; he made this world a better place.

Before she could respond verbally, a knock on the interrogation room door pulled Kate back to reality. She gave the writer one last look before pushing back her chair and walking towards the exit. Just as her fingers curled around the door handle she heard, "Please, Beckett; please believe me," and her heart broke all over again.

Prompt: What if Probable Cause happened after C/B stopped working together after the Headhunters case.