Author's Note: Just what I need, another multi-chapter fic. But seeing as how the humor in season 8 is doing nothing for me (if you're gonna give me angst, go all the way with it), here's my attempt at a post-8x02 fic. It starts in the immediate aftermath of Kate's decision. Spoilers for season 8. Enjoy!

The clock read 3:15. In the morning.

The red numbers on the alarm clock by Castle's bed taunted him in the darkness. Exhausted though he was, Castle couldn't get his eyes to shut. Sleep was far more elusive than it had been in years. The urge to write wasn't keeping him up, nor was the mind-numbing blockage that once led him to kill off Derrick Storm.

No, this… the empty spot on the bed to his right was the source of consternation. Actually, consternation wasn't the right word. Confusion. Anger. Hurt. Feeling like he had been blindsided by an out-of-control 18-wheeler. And on top of it all, a sense of déjà vu to which he dared not give voice.

Because that would make it real. Richard Castle couldn't handle real at the moment.

His stomach churned every time he caught sight of the silver band on his left ring finger, yet Castle couldn't bring himself to take it off. He still couldn't tell anyone, if they had asked, exactly what had happened. Less than a day earlier, he had been filled with nothing but relief and gratitude - both over the fact that his wife was back home safe and from the fact that she had promised him no more secrets.

Not even twenty-four hours.

Not even twenty-four hours before his wife packed a bag, stared at him with tears in her eyes, and spouted some vague nonsense about needing to be by herself. Why? No telling, she didn't say. She asked him if he trusted her, then kissed him and walked out the door.

Castle sat up, kicking off the sheets that had been bunched up over his feet. A faint burnt smell still lingered in his loft, the result of a smorelette long forgotten the second his wife sprung this surprise on him. He hadn't fixed anything else to eat since, too bitter and too emotionally ragged to even think about food.

What changed? What happened in the hours since their reunion in that airplane hangar? How did they get from no more secrets to her walking out the door?

Roughly thirty-six hours ago, Castle thought the worst thing he would have to endure was no longer accompanying his wife to the Twelfth Precinct. Shadowing a captain would have been far different than shadowing a detective, and despite his obvious bond with everyone at the precinct, there was no real need for him there now that Kate Beckett was the one in the fishbowl office.

Still, her promotion had been cause for celebration; this was the next step in her journey - one Castle had unwittingly foretold in the just-released Driving Heat. And for the first time, he wondered to himself if perhaps that was to be the last Nikki Heat book. Critical acclaim hadn't been as boisterous for this book as it had been for the others, and if his inspiration had up and left…

Castle scrubbed a hand over his face. Yeah, that conversation with Gina would be fun.

Pushing himself out of bed - and officially giving up on the thought of sleep for the rest of the night - Castle padded into his office. Distancing himself from her scent, which still lingered on his sheets, did nothing for his mood. If anything, his mood worsened as the minutes crept along; normally, he would mask it with humor, an outgoing childishness that disarmed people.

But in his solitude, there were no jokes. No quips or wild theories or toys. Just a suffocating silence and a mind that kept screaming Why?!

That one question had fueled much of Castle's career; because ultimately, that was what his books examined. Why people did the terrible things they did. That philosophy had only strengthened in the years he had spent shadowing Kate, seeing real-world murders and their all-too-real implications.

What drove people to do what they did… out of all of life's mysteries, that was the one Castle relied on the most. But it wasn't nearly as fun now that he - now that his marriage - was the mystery.

He once quipped that Kate Beckett was a mystery he was never going to solve, but in recent months, Castle had allowed himself to think that he had done a fairly good job. He still didn't know everything there was to know, but their closeness and her openness - in light of finally solving her mother's murder and the drama of his own disappearance - made him think there wasn't much mystery left.

But now… once again, that bastard's words echoed in his brain.

You come in here all on fire about your wife, you don't even know who she is.

Sixteen years, Kate Beckett has been obsessed with solving her mother's murder. You really think she can turn off that kind of obsession?

I'm saying, she's never going to be happy just being Mrs. Castle.

She needs to tilt at windmills. It's in her DNA.

Like a moth to a flame.

Castle was sitting at his desk by this point, pouring himself a glass of scotch. He downed the bitter liquid in one gulp, hissing as it slithered down his throat before chucking the glass across the room. It landed with a thud on the thick carpeting, but the release was momentarily cathartic. Such outbursts were rare, and for Castle to have one, it had to be something serious.

He was glad the loft was otherwise empty; the last thing he needed right now was to try explaining to his daughter or his mother what had just happened. Not just because it was still so painful - he could feel the pressure on his chest - but because he wasn't sure he could find the words to explain it all.

He didn't even know what had just happened.

From his chair, Castle peered out into the foyer. The front door was still open; he hadn't touched it since she left. He had briefly considered going after her, his heart crumbling when he heard a choked sob from the other side of the wall, yet he never moved. Not until he heard the elevator ping to announce her departure from the floor.

She said she loved him. She asked him to forgive her. She never once explained what she was doing or where she was going, but her fingers ghosted over the stubble on his cheeks with the same tenderness she gave in the morning when they were still wrapped up in each other in his bed.

Her lips had the same taste of love and coffee and cherries that he adored. Her eyes, even when full of tears, held as much love for Castle as he had ever seen. And yet… she walked out on him.

She opened that door and she left.

Castle hadn't been this confused since the day Kyra left. With Meredith, there was infidelity. With Gina, there was… well, Castle could say the passion had died, but that assumed there had been any passion in the first place. But this… how could Kate Beckett claim to love him and then turn her back on him?

Unless…

No.

No, that can't be it.

His wife did not just choose the rabbit hole over him. Not again.

But that was the only explanation that made sense. There was no way she could go from shut up and kiss me to forgive me in less than a day. As plot twists went, it was pretty damn steep. Then again, Castle was more emotionally invested in this story than any book he had ever read. This blindsided him in all the worst possible ways, but now that he had at least some of his druthers…

Okay, so Kate wasn't running away from him. But why would she run off to tackle whatever she was tackling by herself? Hadn't she learned over the past six years or so that they were better off together?

She needs to tilt at windmills.

It's in her DNA.

It was a shame William Bracken was dead, because Castle had the sudden urge to have a conversation with his fists and the disgraced Senator's face. Castle was probably one of the least violent people on the planet, but when it came to the people he loved, he was capable of far more than most people expected.

Not that beating Bracken to a pulp would bring back his wife. But if nothing else, the release was welcome.

Pushing himself from his desk, and ignoring the empty glass now on his bedroom floor, Castle grabbed his keys and his coat. What he needed to do couldn't be done here at the loft, and if his theory was correct, then he probably wasn't safe much of anywhere. Not like his destination was any safer, considering the near-shootout that transpired earlier that day, but it didn't smell of his wife, so there was that.

Like a moth to a flame.

And we all know what happens to the moth in the end.

Somewhere…

"Are you sure about this?"

No, she really wasn't.

Fact was, Kate Beckett wasn't sure of a lot of things anymore. What was supposed to be her first day in charge of the Twelfth Precinct - her first day as Ryan and Espo's boss - had turned into her running for her life, nursing yet another gunshot wound, and wishing like hell she could run to her husband.

Instead, she ran away from him. All because the blood of five federal agents was on her hands, and she couldn't stomach the thought of adding to it. She didn't even want Vikram Singh - the man whose phone call started this whole mess - involved in this, but he was as stubborn as her on this. Rachel McCord and the others had been colleagues of his, just as much as Kate, and he was determined to see this through.

Briefly, her determination faltered. It always did when she caught sight of the ring on her hand.

"Kate," Vikram prodded. "You can still back out. I wouldn't blame you if you did."

"That's because you don't know me," she said with a crack in her voice. She kept her back to Vikram, because she didn't want him seeing the tears brimming in her eyes. If he saw how this was gutting her, he would insist even further to tackle this on his own. But that would get him killed, and she was tired of people dying because of William H. Bracken.

Or that partner of his.

"With all due respect, Kate… this isn't your fight."

"The hell it isn't!" Her voice quivered, but the ferocity in Kate's eyes never wavered. Even as a tear ran down her cheek and the finger she pointed at Vikram shook. "Rachel, Hendricks… all of them are dead because of me."

"You couldn't have known –"

"I should've," she argued. "I should've known that one little search would come back to haunt me."

"So let the feds handle it." Vikram was pretty insistent in playing the Devil's Advocate card.

"I can't." Kate began to pace, folding her arms over herself, in part to hide the wedding ring that had been taunting her since she left the loft. Her fingers brushed over her side, catching on her scar under her black turtleneck. She hissed in pain. "I just… I thought this was over. I thought slapping the cuffs on Bracken put an end to this."

"It did," Vikram countered. "You solved your mother's murder. The rest of this? It's not your problem. It is so above your clearance, your pay grade… you are going to be so in over your head on this…"

Kate frowned and stepped toward Vikram. "What are you saying?"

Vikram put his hands up in front of himself in a defensive and conciliatory gesture. "I'm saying… you're worried about whether or not your husband's gonna take you back after this? If you're not careful, he won't have a chance to make that decision."

"Do you know how many near-death experiences I've had over the years?"

Yeah, and just about all of them were with him by your side, the little voice in her head argued - a voice that had not shut up once since she walked out that door and tried to keep from breaking down in the hallway.

"And how many more can you have before your luck runs out?"

Kate dipped her head and bit her lip. Really, what could she say to that? As much as she dreaded the thought of living her life without her husband - honestly, the thought turned her stomach - the idea of Castle living his life without her wasn't much better. If anything, that was worse, because then she would've inflicted the sort of pain on him that she had battled for so many years after her mother's death.

This was a textbook case of every option being terrible, and Kate was left with picking the one she thought was the least bad. As heartbreaking as it was, as much as she shattered at the look in his eyes, walking out on him was the only thing she could think to do that wouldn't immediately put him in the crosshairs.

This was her fight. Not his.

If you have a problem, we have a problem. That's how this works.

This wasn't about trust. She trusted Richard Castle with her life, as much as she trusted her partners at the Twelfth, if not more so. But whoever was pulling the strings on this had killed five federal agents and a disgraced Senator in a maximum-security prison without so much as a sweat. The last thing she wanted was her husband in the crosshairs.

So if she had to break his heart to save his life, so be it. God willing, she would glue the pieces back together herself when this was all over. If he'd let her.

"Look, Kate." Vikram shook his head. "I'll back your play, no matter what you decide. But if you're in this, you have to be all the way in. You can't waiver. All in or all out. Anything in between, and your husband will be planning your funeral."

Kate almost doubled over at the words, choking back the sob that had threatened to escape from the moment she left Castle's building. She clenched her jaw and closed her eyes, trying desperately to reign in the swirling emotions. She was so much better at controlling her feelings when her hair was short and choppy and red.

Standing upright again, Kate sucked in a deep breath and opened her eyes. Training her stare on Vikram, her hands balls into fists. She didn't want to do this; everything in her screamed for her to back out, go back home, and beg her husband for forgiveness.

But she couldn't back out. Not now.

"Then let's make sure he doesn't have to."