(Author's Note: Remember at the beginning where I said that this story took me to some dark places? Just to be clear, although there WILL be a happy ending, things are going to get pretty heavy along the way. Thanks in advance for sticking with me.)

The next few weeks passed in a blur. Castle (he began to think of himself that way, like all of the cops) shadowed Beckett on case after case, some of them boring and prosaic, some fascinating and challenging. Even the boring cases were rich sources of new material, and Nikki Heat's story developed in leaps and bounds.

Beckett was slow to open up, but she let out bits of information in drips and dribbles. When she told him about his mother's death, her father's struggles with alcoholism, he knew those moments were milestones; he was gratified that she had decided to trust him with those parts of her story. And if he felt a twinge of conscience when he talked Esposito into showing him the case file on Beckett's mother's murder, it was subsumed under the rush of fascination for a new puzzle to work on.

Almost every day, Castle made the effort multiple times to make eye contact with Beckett, seeking that connection again, that zing, that ineffable shock to the system that he'd felt the first few times their eyes had met. But somehow he was never able to capture it again, however hard he tried. As time went on, he found himself starting to wonder if he had imagined it.

As for Mickey, the dog continued to show up, not during every case, but frequently. When Beckett was running down the sidewalk in pursuit of a suspect, Mickey came bursting out of a conveniently placed alley, tackling the suspect and bringing him down. When Beckett and Castle were interviewing a witness in a bar and a fight broke out between two other bar patrons, somehow the dog was there again, shoving his huge body between the fighters to separate them so that Beckett, and the backup she had hastily called, could subdue them. Again and again, Mickey turned up and put himself between Beckett and danger.

Castle couldn't quite understand it, because Mickey was clearly Beckett's personal pet, not an NYPD-issued canine officer; she never brought him along when they went out to interview suspects or witnesses; he never came into the precinct with them. Yet, he seemed to keep turning up. Castle supposed that the dog was biologically programmed to protect his person, which made sense, but it was almost uncanny how often he appeared at just the right moment.

And there were times when Mickey didn't appear at all. On one memorable occasion, they went to an apartment to interview a potential witness. As soon as Beckett knocked on the door and called out "NYPD," the door exploded outward and a young man came flying out with a huge butcher knife in his hand. Beckett's quick reflexes had her ducking aside just in time to avoid getting skewered, while Esposito and Ryan yanked Castle back out of the way, all three cops reaching for their guns.

The attacker dashed into a nearby stairwell, and they all pursued him up, up, up the stairs and out onto the roof of the apartment building. There, the young man dropped the knife with a clatter, but ignored the cops' shouts of "Freeze!" and "Get on the ground!" and so forth. Instead, he ran to the edge of the roof and attempted a daring leap to the roof of the building next door.

Unfortunately for him, that kind of maneuver wasn't nearly as easy in real life as it looked in movies, so he never made it across. He fell into the gap between the two buildings and landed on the pavement below. Castle and the three cops ran back down the stairs as fast as they could, but there was nothing they could do for him.

Castle stood with his eyes averted from the body. It wasn't the first time he'd seen death, but having been right there when it happened was a different feeling.

"Your first really messy one," Ryan commented. "You okay, Castle?"

"Yeah," he said, focusing on Beckett's profile as she stood looking down at the body, talking on her cellphone to the M.E.'s office. "I'll be okay."

"Beer is the answer," Esposito said. "Tonight, after shift." Seeing Castle's face light up, he added, "You're buying."

"Deal," Castle agreed, grinning. He knew that the cops often went out for a beer after work, but he had never been invited along before, so this was an encouraging sign of being accepted into their ranks.

Beckett ended the call, looked at her watch, pursed her lips, looked around at the scene, checked her watch again. Then she said to Esposito, "You got this?"

"Yeah, sure."

"Good." And to Castle's surprise, she turned and walked away.

"Where's she going?" he asked Ryan, who shrugged.

"Beats me." The detective didn't seem concerned, so Castle shrugged it off as well. He stood aside and took notes while Ryan and Esposito handled the processing of the scene.

By the time they got back to the precinct, Beckett had returned as well, and was busy updating the murder board.

"Where'd you disappear to?" Castle asked her, and got a bland look in response.

"Had an errand to run. What've we got on our jumper?"

At the end of shift that day they all went to a nearby cop bar, where Beckett, Esposito, and Ryan regaled Castle with their goriest, most gruesome stories from all their years working Homicide. It was hideous and fascinating.

Beckett bowed out early, but Castle stayed at the bar with the boys for several more beers. And as they were all starting to feel the effects of the alcohol, a thought flew into Castle's head and out of his mouth all at once: "Hey, guys. How come Mickey wasn't there today?"

"Who?" The two cops looked confused.

"Beckett's dog. You know." He made a vague gesture toward the floor, trying to indicate the size of the animal. "Big black dog. Mickey."

"Oh, right." Ryan blinked fuzzily. "What about him?"

"How come he wasn't there today? At the apartment with the guy. With the knife."

Ryan and Esposito stared at him expectantly, as if he were telling a joke and they were waiting for the punch line. He stared back, too tipsy to understand their reactions.

After a long moment, Esposito sat back and said, "I don't know, bro, maybe he couldn't get a taxi." And they all burst into raucous laughter.

The next morning Castle awoke with a mild hangover and only the vaguest recollection of the conversations they'd had at the bar. In the rush of getting Alexis to school and himself to the precinct, he didn't give it any more thought; it faded to a blur at the back of his mind. They closed that case, and moved on to the next one, and then the next.

"Is everything okay?" Castle asked, one afternoon toward the end of shift. Beckett had been distracted all day: staring into space, looking at her watch and frowning, checking the police scanner and the arrest database on her computer, tapping her fingers, chewing her lower lip. Something was definitely bothering her.

She didn't answer right away, and he almost wondered if she had heard him; but after a long moment, staring at the surface of her desk, she admitted softly, "It's Mickey. He's... a little under the weather."

"Oh," Castle said, feeling his eyebrows lift; the words themselves were concerning, but it was also always a welcome surprise when Beckett revealed anything personal.

"I'm sure he'll be fine," she added, her tone just a little too upbeat to be believed, but then her voice lowered again: "It's just..." She paused, took a breath. "It's just, after my mom died, for a while there, Mickey was all I had. You know?"

"Yeah, of course."

There had never been pets in Rick's life as a kid, although he had spent time with dogs, even done some dog-sitting for friends in his younger adult years. So he thought he understood that bond, the unconditional love of an animal, the way a pet could bring a kind of comfort that another person never could.

And his writer's imagination could see all too clearly just how alone young Kate had felt, with her mother gone into the ground and her father gone into the bottle. It would have been natural for her to turn for comfort to Mickey, who clearly loved Kate as much as she loved him.

Beckett was back to fidgeting and fretting, so he asked tentatively, "Do you think you need to take him to the vet?"

"What?" She startled out of her distraction, frowning over at him. "Oh... no. He'll, uh, I think he'll be okay."

Just then, an alert chimed from Beckett's computer. She whirled toward it, her eyes skimming swiftly across the text as she clicked through the system.

Castle watched in bemusement as she suddenly straightened and sharpened, lifting her head to scan the bullpen, zeroing in on a uniformed officer who had just gotten off the elevator.

"Hammond!" she called, and the uniform looked around, then came trotting over.

"Detective?"

"Did you just get back from a Robbery bust?" Beckett asked, her voice quivering with a low urgency that neither Castle nor Hammond understood.

"Uh, yeah?" the young uniform responded, confused. "They had a raid on a warehouse downtown, needed help clearing the scene."

"I heard there were casualties," Beckett said. Hammond nodded confirmation.

"Yeah," he said, "there was some shooting before we got there, and one of the suspects went down. The M.E. has him. Something wrong?"

"No. No," Beckett said. "Sorry, go file your report. Thanks."

"No problem," the young man replied, and even as he was turning away, Beckett was already grabbing her coat, reaching for the drawer where she kept her purse.

"Beckett?" Castle queried, and she jumped a foot, startled, as if she had entirely forgotten he was there.

"Castle," she gasped, putting a hand briefly to her chest. "I... I have to go."

"Is it the-" but she was already gone.

Castle had a head full of questions and nothing to do with them, so he did the only thing he could: he went home. A pleasant evening of playing dress-up with Alexis quieted his busy brain temporarily, but once she was safely in bed, all of his questions came flooding back.

He sat down at his desk but didn't open his computer yet. Instead, he just stared into space for a while, letting the thoughts flow.

Beckett was worried about her dog's health, but she didn't want to take him to the vet. Mickey was an older dog, that much Castle knew; he remembered Montgomery's surprise to hear that Beckett still had him. And Beckett had said that Mickey comforted her after her mother's death, which had been more than ten years ago now.

So Mickey must be at least eleven years old, right? Wasn't that pretty old for a dog? Frowning, Castle opened his computer and began a web search.

A while later, after having spent rather too long trying to figure out what breed of dog Mickey was, he sat back again with a grimace.

It seemed like the dog must be nearing the end of his life, and Beckett must know that, surely. So why was she hesitant to take Mickey to the vet? Was she just reluctant to hear a medical professional tell her what she already knew? The way she had talked about Mickey comforting her after her mother's death... it must be hard for her to think about losing him. Yet, wasn't that something every pet owner eventually had to face up to? Beckett was the pragmatic type, so living in denial didn't seem like her style.

Rick thought back to all of the times he'd seen the dog recently - running, jumping, bounding up and down stairs, tackling suspects. Mickey certainly didn't move like an elderly dog. He seemed strong and fit, with endless energy. Maybe he was some rare breed that lived longer than average?

His head still buzzing, Rick opened a new window and began to write a new scene. Maybe he would have Nikki Heat adopt a dog...

The next morning, Beckett seemed much calmer, her tension from the previous day apparently gone. Castle had meant to ask her how Mickey was doing, but it went forgotten in the excitement of a new case. This one involved vodun, giving Castle an opportunity to flex his esoteric knowledge in front of Beckett and the boys, which was always satisfying.

Beckett grudgingly agreed to come back to his loft to find some of the research he had done for Unholy Storm. Along the way, he placed a quick phone call to Michelle, the restaurateur and vodun practitioner who had been his primary source for that book.

When he opened the door to the loft and Michelle got her first look at Beckett, her eyes widened and darted from Beckett to Castle and back again. Michelle muttered something in her native language and made a complex hand gesture. Glancing over at Beckett, Rick saw that she was just as confused as he was.

But then Michelle relaxed, and stepped forward with her usual friendly smile. "Someone order lunch?"

There was a tension between the two women that Rick couldn't understand, simmering below the surface the whole time they were eating and discussing the case. When they were done, he walked Michelle out, and she paused halfway out the door to look back at him with a slight frown creasing her forehead.

"Be careful here, Ricky," she admonished, keeping her voice low. "You don't know what you're dealing with."

Why did he get the feeling she wasn't talking about the case? But before he could ask, Beckett's phone was ringing with the news that there was another victim, and they were back in action.

And this case ended the next day in a shootout, entirely unexpected and completely terrifying. Rick found himself crouched behind a stranger's kitchen island with Beckett, his entire body tense and on edge, waiting for the suspect on the other side of the room to start shooting again.

"I need a clean shot," Beckett hissed. "I gotta get eyes on him somehow."

Rick's gaze landed on the wine rack, and he was just beginning to formulate a plan when they both heard a new sound from the hallway outside the apartment. It sounded like a low growl, followed by a fierce warning bark.

"Mickey," Beckett murmured as if to herself, and before Castle could react, she stood up, exposing herself, gun at the ready.

Luckily, the dog had distracted the suspect, and when Beckett emerged from behind the island, the suspect's head was turned away. She took the shot without hesitation, and Mickey immediately bounded over to pin the man down with his bulk.

Beckett dashed forward to check on them while Rick was still blinking and reeling, his brain trying to catch up to what had happened.

Within minutes, the now-familiar crowd of CSU and uniformed cops began to swarm the area, taking away the injured suspect and beginning the work of processing the scene. Castle leaned against the wall, trying to stay out of the way, watching Mickey do the same at the other end of the hallway.

Beckett, having finished supervising the suspect's removal to the ambulance, came back down the hall to rejoin Castle outside the apartment door.

"You okay, Castle?"

"My first gun battle," he mused, still feeling the lingering effects of the adrenaline.

"Your last gun battle," she corrected with steel in her glare.

"Don't be so pessimistic," he grinned. "I think I handled myself pretty well."

"Yeah," she conceded, "you probably saved my life."

"Probably? I definitely saved your life. Although Mickey helped too, of course," he added, inclining his head in the direction of the dog. "I guess he's feeling better, huh?"

"What?" Beckett gasped, turning to look at Mickey, then turning back to Castle, her face showing a degree of shock that he didn't understand.

"Yeah," he said, surprised, "I mean, I was working on a plan for distracting the guy, but then Mickey took care of it. He really has a knack for showing up at just the right moment, doesn't he?" He paused, then, a frown beginning to form on his face as he heard his own words and felt a number of mysterious puzzle pieces start to slot into place. "He always shows up..." he repeated, almost to himself.

Beckett was still gaping, a series of indecipherable emotions flickering across her suddenly pale face. "You... you can see him?"

Rick blinked. "Well, of course I can see..." He trailed off, looking at her in confusion. "What do you mean?"

"I..." Turning, Beckett caught the attention of a uniformed officer who was just coming out of the victim's apartment. "Perez, have you seen my dog?" Subtly, she angled her body so that Officer Perez's line of sight was down the emptying hallway, directly toward where Mickey sat.

"Your dog, Detective?" Perez was clearly confused. "Uh, I think you might have brought him to the precinct picnic last summer?"

"Right," she agreed. "Thanks."

"No problem." And the uniform proceeded to walk down the hall, passing directly by Mickey, without ever looking at the dog or acknowledging his presence.

It was Castle's turn to gape, watching Perez go; and now that he started to pay more attention to the other cops and support personnel who were coming and going around the crime scene, he noticed that none of them looked at Mickey or acknowledged him in any way.

Suddenly he found himself thinking about all the other times Mickey had shown up, and trying to remember whether any of the other cops or witnesses had mentioned the dog, or interacted with him. Aside from the suspects whom Mickey had physically touched in some way, Castle couldn't remember a single person ever acknowledging the dog's presence. And then there was the way Espo and Ryan had reacted when he'd asked about Mickey that time at the bar...

Baffled, he turned back to Beckett, meeting her eyes again. As soon as their gazes locked, he felt again that electric shock of connection, which he'd felt the first few times they met, but not again since. It drew a startled gasp from his throat, and Beckett recoiled slightly, blinking in surprise; he wondered if she had felt it too. He wondered if he looked as pale and shocked as she.

"What the hell is going on here?" he asked, keeping his voice low, canting his body toward her. "Beckett? Is your dog... magic?"

"Castle..." She looked younger and more uncertain than he had ever seen her, chewing her lower lip, clearly struggling with something. "Listen, I need to finish up here and file my report, okay, but then... can we talk? Later?"

He frowned again, but decided that she wasn't trying to brush him off - and if she was, he wouldn't let it happen this time. All kinds of half-baked theories were already crowding into his brain, and he wasn't going to be able to rest until he knew the true story.

So he said simply, "Okay," and walked away.