A week went by. Then another.

After the first few days, Rick didn't bother trying to contact Beckett any more. She'd rejected all of his phone calls, ignored his voicemails and emails and texts, instructed Ryan and Esposito not to talk to him.

He decided it was just as well, because he didn't have any idea what to say to her anyway. He kept replaying in his mind that last devastating conversation in the hospital hallway, after he'd tried to show her what he had found about her mother's murder.

That's it. This is over, she had said. Flat tone, flat expression, not a crack in the armor.

I trusted you, she'd added after a beat. I thought you were- but she'd cut herself off there, shaking her head slowly. It doesn't matter. We're done.

And she'd walked away.

Alexis was the only thing that kept Castle from drowning himself completely in alcohol. No matter how far down he got, he wasn't going to cross that line. He was still there every morning to get her up and take her to school, even if he hadn't slept all night. Even if, as soon as she disappeared inside the school building, he went straight back to the loft and opened another bottle. He always managed to sober up enough by the afternoon to pick her up and bring her back home, spend the afternoon and evening with her, then go right back to the bottle as soon as she was asleep.

And if the total oblivion of alcohol was off-limits to him, fate (or whatever might be pulling these strings) cruelly denied him the oblivion of sleep as well. When he did manage to shut up his self-recriminating brain long enough to drift off, his dreams were full of shapeless, nameless horrors, shrieking in his ears until he clambered unwillingly back up to wakefulness just to escape the nightmares.

He knew that Martha was worried about him, but he fended her off; she pursed her lips, threw up her hands, and mostly left him alone.

Midway through the third week, he decided to write Beckett a letter. Cheesy, corny, old-fashioned? Yeah, sure. It was all of those things. But the written word was his milieu, after all, and if nothing came of it, at least he would have tried.

It took a few days' worth of detox - caffeine gradually replacing the alcohol in his bloodstream - but he finally managed to get a few good paragraphs down. Now all he needed was the hook, the twist. Apologies were well and good, but what then? How could he convince her to take him back?

It was another late night, the surface of his desk littered with half-scribbled-on pieces of paper, when he heard a strange sound. Blinking blearily, he put down his pen and listened.

There - he heard it again, coming from the front door of the loft. Rising unsteadily from his desk chair, gasping slightly at how stiff and sore his muscles were - how long had he been sitting there? - he made his way through the living room and toward the door, listening, straining with all his senses.

It sounded like something scratching, scratching rhythmically on the door, and his blood sizzled in his veins with dread, but pure maniacal curiosity kept him moving forward. His hand reached out, closing around the doorknob -

The door popped open and there was Mickey.

Castle stood staring in disbelief. The dog looked up at him, expression as serious as he had ever seen it. His deep liquid eyes were full of concern, and he gave a bark that sounded somehow commanding.

"Mickey?" Castle said stupidly, a rush of cold sweeping over him, making him shiver as the adrenaline drained away. "What the hell? I mean, come in."

But Mickey wouldn't come in. He stood up and gave Rick an expectant look, barked again, turned as if to walk away down the hall, but looked back at Rick again. The message was clear: he wanted Rick to follow him.

"I..." Rick looked down at himself and grimaced. His boxers and t-shirt were grimy, his feet bare, his chin probably gone past scruff and almost into caveman territory.

He had a feeling he knew where Mickey wanted to take him, but he couldn't go like this.

"Look, Mickey, I gotta get cleaned up first, okay?" He looked at the dog. The dog looked at him.

Rick remembered back to that first meeting, so many months ago, when he'd felt like an idiot talking to a dog. But that was before he knew... everything he knew now.

Now, he could only hope the dog really did understand more than he should.

"I'll go to her, okay? I will," he said. "I just need a shower, and I gotta take care of Alexis. Then I'll go over there. I swear."

Mickey's ears perked up at the sound of Castle's daughter's name, and he seemed to come to a decision. He stepped forward and licked Castle's hand. Then he turned and padded away down the hall.

Rick hurried back into his study, and through it to the bedroom and bathroom beyond. He took the fastest shower ever, shaved hastily, and pulled on some clean clothes.

He tiptoed quietly up the stairs, past Alexis's door, and rapped softly on Martha's. She was up, of course, watching TV with the sound turned down low.

"I have to go out, Mother," he stage-whispered. "You're in charge here, okay?"

"Is it Katherine?" she asked, half-rising from her dramatically reclined position on the bed, but he gestured her back down.

"Yeah, it is. I'll... I'll tell you about it... sometime," he evaded. And before she could ask any other too-incisive questions, he made his escape.

Somehow, it just wasn't a surprise to find Mickey sitting patiently next to Rick's SUV in the parking garage.

"Just me and the magic dog," he joked weakly to himself as he unlocked the car. Mickey yipped disapprovingly.

"Sorry. Hop on in."

It was late at night, but it was New York City, so there was as much traffic as ever. Still, it didn't take long to get to Beckett's neighborhood, and he found a parking space without too much trouble.

Mickey hopped out of the car and led Rick up the stairs, down the hallway, to Beckett's door. Where Rick stopped, wavering, dithering.

Shit. What the hell was he supposed to say? He should have brought his half-written letter, damn it. At least it would have given him a starting point.

Mickey whined and nudged him. The dog was big, a solid chunk of muscle; his nudge nearly knocked Castle over.

"Okay, okay, boy, geez. Give a guy a minute to collect himself."

But even before he could lift his hand to knock, the door opened, and there she was.

"Mickey?" and then she caught sight of Castle and her expression hardened. "What the hell are you doing here?"

Mickey grumbled and nudged Castle again. He stumbled forward, nearly falling onto Beckett, but just barely managed to catch himself on the door frame while Kate flinched back out of range.

"He came and got me," Castle said defensively, still clutching the door jamb. "Scratched on my door and made me come over here."

A frown furrowed Beckett's forehead. "He did?"

"Beckett - Kate - please listen." Rick straightened up, moving fully into the apartment, the dog slinking in alongside him. He closed the door behind him, his gaze fixed on her. "Please, just let me tell you-"

"There's nothing to tell. I don't-" but Mickey interrupted her with another warning rumble, moving to stand by her side and press his body against her leg. Her hand landed naturally on his head, petting him lightly, grounding herself.

"Just let me tell you how sorry I am," Rick said softly. "I fucked up, and I know it. I'm so sorry. Please tell me how I can make it up to you."

"You can't," she said, but not as flatly as she had probably intended. She stood, one arm wrapped protectively around her ribs, the other hand still mindlessly stroking the dog's head. "I clearly told you to leave my mom's case alone. I trusted you."

"I know. I know, and I'm really sorry, but if you looked at what I found-"

"It doesn't matter what you found. I told you, I put all that behind me."

"I just didn't want you to feel like you failed," Rick said quietly. "I just... thought I could help. But what I did was wrong, and I should have respected your wishes."

He sighed and turned toward the door. "I'm sorry I bothered you."

But before he could reach the door, Mickey was there again, putting his body in the way. Giving another yip, he nudged Rick yet again, pushing him farther into the apartment.

"Mickey!" Beckett scolded. But the dog looked her right in the eye and yipped again. She scowled at him, then transferred the scowl to Rick.

"I... guess he likes me?" he said, trying a tentative version of his boyishly-charming smile. It just made Beckett's frown deepen, but she threw up her hands in surrender.

"Whatever. Fine, you can come back to the precinct tomorrow." She shot another glare down at the dog. "Satisfied?"

Mickey apparently was. He sat down, tongue hanging out of his mouth in a goofy smile, tail slapping happily on the floor. Beckett huffed incredulously.

"You really are something," she told the dog. And to Castle, "Don't think this means I'm not mad at you any more."

"I won't," he promised, backing toward the door again, keeping a careful eye on the dog. "Take all the time you need." He opened the door, checking again to see if Mickey was going to object. But the dog seemed perfectly happy to sit next to Beckett and watch Rick go.

"Until tomorrow," he said, and left.

He went back to the loft, and for the first time in weeks, slept deeply and dreamlessly all through the night.

And so their rhythm resumed. If anyone at the precinct was surprised to see Castle back, they didn't show it, and soon enough there was a new interesting case, and then another, and another.

All those sleepless nights of writing finally came together, and Heat Wave was released, to rave reviews - far and away the most successful Richard Castle book yet. He was already deep into writing the sequel, and it felt like there was a bottomless well yet to be plumbed, the inspiration he drew from Beckett itching at his brain night and day.

Mickey, of course, still showed up on his own schedule, always at the right moment, when Beckett was cornering a suspect or conducting a raid or whatever the case called for. The dog always seemed fit and healthy when Castle saw him, and he knew it was because he only saw Mickey when things were going well - when the dog had another spirit inside him, keeping him going.

On the other hand, Rick found that he could tell when Mickey was having a bad day, because Beckett's mood would show it. She grew snappish and impatient, fidgety, constantly checking the police scanner for news. When something promising came through, she would rush out of the precinct as fast as she could, and the next day she would be calm again, and Castle knew it meant that another criminal had died and was inhabiting Mickey's body, keeping him strong and healthy for another little while.

Beckett still refused to talk about it, shutting him down instantly whenever he tried to bring up the subject. He knew that the strain of worrying about Mickey during the in-between days was taking its toll on her, and wished there were something he could do... anything he could do. But his research had gone nowhere, and he was out of ideas.

They caught a case that involved Rick's ex-girlfriend Kyra on her wedding day to another man. Once, Rick would have called her the love of his life; but reuniting with her over the murder of one of her bridesmaids made him realize he hadn't had a clue what love really was, back when he'd been with Kyra. What could he have known, all those years ago, as young and stupid as he had been? He'd thought he would never love another woman as much as he'd loved Kyra, and had spent years believing that. But now he knew it wasn't true.

Now he knew that he was falling in love with Kate Beckett.

Then there came a morning when they caught what seemed at first like an ordinary, albeit somewhat Beckett-flavored, murder case. The victim was a lowlife named Jack Coonan, dead from a number of stab wounds. They quickly uncovered a connection to organized crime and gang rivalries, and began trying to run down the details.

Beckett was grouchy and short-tempered, in a way that Castle knew could only mean one thing. "How's Mickey doing?" he asked quietly, in the car on the way to the next interview. She scowled and shot him a sidelong glare before returning her attention to the road.

"It gets harder every time," she gritted out. "Even with all the meds the vet gave me. He's just... tired."

"I bet he is," Castle murmured, studying her profile with concern. She was tired herself, though she hid it well. "Do you think-"

"Leave it alone, Castle," she said sharply. "We're on a case."

But the next day, the case took a turn that none of them had seen coming.

Lanie had realized, and called Dr. Murray to confirm, that Jack Coonan had been killed by the same person who'd killed Beckett's mother all those years ago.

Beckett was stunned, reeling from the revelation. After a short conversation with Captain Montgomery, she went running out of the precinct, leaving the rest of them in turmoil.

The urge to run after her was powerful, but Castle knew better by now. Kate Beckett needed time and space to process her feelings, alone. He caught Lanie's eye and saw that she had been watching him, ready to stop him if he tried to follow Beckett.

"It's okay," Castle said to Lanie, to the rest of the team, to himself. He cleared his throat. "It's gonna be okay. Let me buy you all a beer."

Dr. Murray declined, but Ryan, Esposito, Lanie, and Montgomery accompanied Castle to the nearest cop bar, where they all drank beer and talked awkwardly and self-consciously about almost anything they could think of, other than Beckett, until they all ran out of topics and wound down.

It was the captain who stood up first, draining the last of his beer and setting the empty bottle down on the table. "Get some rest, everyone," he instructed. "If Beckett can't handle it, tomorrow this case is gonna be on you to finish."

Esposito and Ryan exchanged a loaded look, but all they both said was "Yes, sir." And the group dispersed.

But the next day, Beckett resurfaced. Her composure was back - though Castle was sure it was costing her a lot of effort to maintain it - and they were back on the case with a vengeance.

Too late, much too late, they realized that the true killer was Dick Coonan, Jack's brother. But when they confronted Coonan, he was prepared; before Beckett could react, Coonan had Castle in his grip, a gun pressed into Castle's ribs. Beckett's face was white, struggling to stay calm as Coonan ordered them to walk him to the exit.

The muzzle of the gun was a hard insistent pressure in Castle's back, drawing his full attention; it was almost impossible to think about anything other than that tiny, lethal piece of metal, the way the bullet could rip into his body, the unimaginable pain. But through his terror he did manage to find space for two other thoughts: that Mickey couldn't help them because he was between souls right now, and that Coonan hadn't told them who had hired him to kill Beckett's mother.

There had to be a way to get him to give up the information before he escaped. There just had to.

Then Montgomery stepped out with his gun drawn, and Castle heard the despair in Beckett's voice as she begged her captain to stand down.

It all happened in a blur. Montgomery lowered his gun - Coonan loosened his hold on Castle for an instant - Castle headbutted Coonan's face - Coonan's gun came up - and a shot rang out.

It took a heartbeat that lasted an eternity for Castle to realize that the sound he'd heard had been Beckett's gun. Beckett had shot Coonan. She'd given up her chance to find out who ordered her mother's death - sacrificed it to save Castle.

He watched in growing horror as Beckett, openly sobbing, tried desperately to perform CPR on Coonan. It was obviously too late, and within moments, paramedics had arrived and confirmed it.

Beckett was still crying, heedless of the entire precinct watching, as one of the EMTs gently took her aside and began cleaning the blood from her hands with a wet wipe. Castle hovered nearby, feeling more helpless than he thought he had ever felt in his entire life.

All of a sudden Beckett's head snapped up and her eyes met his, filled with fresh dread so intense that Castle flinched backward from it.

"Mickey!" she gasped.

Before anyone else could react, she had grabbed her purse from the floor and dashed out.

Castle felt bile rising in his throat as he realized what Beckett had already concluded. Mickey had been without a second spirit inside him for a few days now - getting weaker and weaker. And now, Dick Coonan was dead.

No. It couldn't possibly. Would a demon be that cruel?

Of course it would, he told himself with an angry toss of his head. It was a demon. Cruelty was the whole point.

Ignoring the questions and demands that Montgomery and the other cops were barking at him, Castle rushed out in Beckett's wake.