By the time Castle got to Beckett's apartment, she was already there - but she hadn't gone inside. He found her sitting on the floor outside her door, knees drawn up and her face pressed against them, shoulders trembling.

"Kate," he murmured, sinking to his knees next to her. She lifted her head, face streaked and stained with tears.

"I can't do it, Castle. I just can't."

From inside the apartment, he could hear Mickey whining plaintively and scratching at the door. The dog's voice sounded weak and thready, and even without seeing him, Castle could sense how elderly Mickey was feeling.

"Kate," he said again, hopelessly, because he had no idea what to say.

"The minute I go in there, Coonan's soul will go into him," she moaned. "And then I have to live with him? Let the man who killed my mother share my dog's body? Let him help me?" she spat, anger struggling to pierce through the despair. "I can't do it."

"You can't stay out here forever." Tentatively, he shifted to sit next to her, and put his arm around her shoulders. He wondered if she would recoil and push him away, but she leaned into him, dropping her head onto his shoulder.

"It's too much," she whispered. "He's taken it too far."

He? That must mean the demon, Castle realized. "Have you ever tried summoning him again?"

"What for?" she sighed. "What good would it do? I don't have anything left to bargain with. No leverage."

Castle pressed his lips together. He had a few answers in mind, one of which seemed simple and obvious, but he wasn't sure if Beckett could handle hearing it.

But almost as if she heard his thoughts again, she shifted against him and said slowly, "I could tell him I want out of the deal. Tell him... to let Mickey die." Her voice faltered on the last word, and she swallowed thickly.

"Would... would that work?" Rick asked hesitantly. The thought was painful - he'd come to care about Mickey too - but maybe it was a way out.

"Probably not," she said, sighing again. "Demons don't just let you out of a deal."

That fit with everything Rick had found in his weeks of research. But of course, it wasn't the whole story.

"What if..." Rick paused, apprehension beginning to rise in his chest. One of the other answers he'd come up with had risen to the forefront of his mind. One that he hadn't dared to even think about very closely, let alone give voice to... but it was now or never.

Sensing the change in his tone, Beckett straightened up, pulling away so she could look at his face. "What?" She frowned, and he knew she was trying to read his mind, but with no success. "Castle?"

"What if," he said slowly, his mouth dry, "you did have something to offer him in exchange?" He swallowed, took a deep breath, and let the thought out. "What if you offered him a different body to put the souls into? Then Mickey could rest, at last."

"A different body?" she repeated, puzzled. Rick could see that she wasn't getting it, so he'd have to make himself perfectly clear.

"Me. I mean me, Kate."

Her eyes went wide. She drew back in shock, jaw dropping, horror flooding her eyes. It was a pretty good representation of how he'd felt when he first thought of it, late one night when everything had been dark.

"Castle, no. You've got to be kidding me."

"I'm not," he said, though his guts felt like jelly. "Listen, it makes so much sense. Think about it. Unlike Mickey, I would understand what I was getting into. And I'm young and healthy, I could do this for a lot of years before I start to feel..." He gestured toward the door, behind which they could still hear Mickey whining and scratching.

"No," she said again, emphatically, but he barreled onward, though he wasn't entirely sure which of them he was trying to convince.

"I'm already shadowing you, so it would be easy for the spirits to use me for their good deeds. Whatever the magic is that makes him invisible at crime scenes, it wouldn't be necessary. Everyone would just see me, helping you. Your partner."

"No!" Beckett said yet again, shaking her head firmly. "Castle, stop. This is crazy." She scrambled to her feet, wiping the backs of her hands impatiently across her cheeks. "You have a family, a child. You can't invite murderer souls into your body, that's insane."

"Mickey manages it," he pointed out, getting to his feet as well. "He doesn't let them take over, except in those moments when they're helping."

"He's a dog. It's not the same thing." She shook her head again, rejecting the idea. "Castle, you can't do this."

"Then what, Beckett? What other options are there?"

She stared at him for a long moment.

"I don't know," she said at last. "I don't know."

The key to her apartment was in her hand, but the hand trembled. Gently, he took the key from her and unlocked the door himself.

Mickey's tail wagged feebly when he saw Castle in the doorway. But then Beckett came in, and as soon as she and Mickey looked at each other, the dog's body went rigid.

Beckett dashed forward to catch Mickey before he fell over. Tenderly, she lowered his huge body to the floor and took his head into her lap.

The dog began trembling all over; Rick startled forward, heart in his throat, but Beckett didn't seem alarmed. This must be what it always looked like when they went through this process.

His instinct was to look away, but he forced himself to watch, imagining how it felt. How it would feel, when it was his turn.

In just a few moments, it was done. Mickey relaxed, and Rick could already see that he looked stronger, healthier. The dog scrambled to his feet and licked Beckett's cheek.

She exhaled softly and hugged him, but her expression was clouded. She pulled back after a moment, holding Mickey's face between her hands, staring into his eyes.

"Anything?" Castle asked, torn between fascination and horror.

Beckett gazed for another moment, then slowly nodded her head.

"Yeah. It's him," she said, releasing Mickey. "It looks the same as it always does, but I know. I just know." She slumped back down onto the floor, her mouth twisting unhappily. "My mom's killer is in there, Castle."

"Could we... ask him?" Curiosity won out and Castle moved closer, staring down at the dog, who looked calmly back at him, tail waving leisurely in the air. "Can we somehow talk to Coonan, get him to tell you who hired him?"

"I don't think it works that way," Beckett said tiredly. "At least, I gave up trying to communicate with the spirits after the first few times. It never seemed to work."

"Hmm." Castle leaned over and scratched behind Mickey's ears. The dog looked up and met his gaze, and this time Castle definitely saw a flash of hard, cruel steel overlaying the usual friendly liquid brown.

Castle shivered involuntarily. He couldn't explain it, but he just knew, like Beckett had, that he was looking into Dick Coonan's eyes. The eyes of a cold-blooded killer.

"It'll be okay," Beckett said unconvincingly, getting to her feet. "Maybe it won't take very long. Maybe Coonan will... do what he needs to do and move on quickly."

"Kate, no. You shouldn't have to live with that. Not when there's another choice."

She looked over at him, her brows drawn down resolutely. "I won't give you to him, Castle. It's not an option. But... maybe you have the right idea."

He frowned. "What do you mean?"

"Maybe offering the demon another body would work," she said. "Mine. It makes the most sense. He can put the murderers in me, and that way no one else has to suffer."

"No!" Castle exclaimed, closing the distance between them. Touching wasn't a thing they did - the moment they'd just had in the hallway notwithstanding - so he didn't, although he was itching to grab her shoulders and shake some sense into her. "Kate, no. Don't do that to yourself."

"Better me than you," she asserted. "I made this mess, my stupid decision all those years ago. I won't drag you into this."

"Drag me? I put myself into it," he pointed out. "And anyway, this part," he gestured toward the dog, who was watching them argue with concern in his eyes, "this is all my fault. If I hadn't hired Dr. Murray to look at your mom's case file - If I hadn't put up the money for Coonan - If I hadn't tried to play the hero and made you shoot him-"

"Stop." Now it was Beckett who moved closer, reaching out to put her hand on his arm, staring up at him. "This isn't on you. At least now I finally know who killed my mom, even if I still don't know why, or who's really responsible. I'm further along toward the truth than I ever managed to get, and that's partly because of you."

She glanced down at Mickey, and that softness came back into her face, her affection for the dog shining through despite everything. "Besides," she added, "I never realized how much it would help just to have someone else who knew about this - about him." She looked back up at Rick. "So I owe you for that too."

Their eyes met, and yet again he felt that flash of fire, that electric spark of connection between them. Her hand burned on his forearm, a single point of contact that felt like everything.

Then Mickey gave a soft whuffle, pressing himself against both of their legs together. They broke eye contact, the moment passing them by.

Beckett looked down at her dog, her lips twisting in displeasure. "Coonan," she muttered. "Why can't you just go to hell?"

Mickey blinked, gave a short bark. His whole body twitched suddenly, as if he had lost control of it for a moment. He barked again, shaking his head as if to shoo away a fly.

"Is that normal?" Castle asked, seeing Beckett's concerned frown.

"It looks like how he used to be in the beginning," she mused, "when he and the spirit would fight each other for control of the body. But they haven't done that in years. He usually convinces them to cooperate right away."

At their feet, the dog whimpered and twitched again, the convulsion looking like a miniature seizure. Castle winced; it was uncomfortable to watch, and he could only imagine how it felt for Mickey.

"What should we do?"

"I don't know." She chewed her lower lip. "Coonan must be fighting him. Maybe he needs to lie down and ride it out."

She began to move toward the living-room area, urging Mickey to follow. "Come on over here, boy. Come lie down."

On the floor between the sofa and the TV, there was a huge dog bed taking up most of the space. Castle noticed for the first time that the TV was on, the volume turned down low. A commercial was playing at the moment.

"You leave the TV on all day?" he asked, watching as Mickey followed Beckett's beckoning hand and went over to lie on the dog bed. The dog was still twitching and making erratic little noises of distress.

"Yeah," Beckett said distractedly, her attention on the dog. "Mickey likes it on, to keep him company while I'm out."

"Ahh, okay." Castle turned to look at the dog again, just as the commercial on the TV ended and the afternoon news anchor came back on the screen.

"In political news, Senator William Bracken was at the State House this morning to introduce new legislation..."

The picture changed to show a group of men walking down the hall of the legislative building, talking.

All at once Mickey leapt to his feet, his entire body tense and quivering. A low, fierce growl came from his throat, more menacing than Castle had ever heard from Mickey all this time.

Castle blinked, the back of his neck prickling at the sudden change in the dog's demeanor. Beckett seemed equally startled.

"Mickey?" she asked tentatively. "What is it?"

The dog, of course, didn't answer. He was fully fixated on the TV, growling and snarling continuously, his front paws moving on the floor as if they wanted to run. He shook his head violently back and forth as if trying to dislodge something, his body still occasionally spasming, never taking his eyes off the TV all the while.

On the screen, the politician began to speak. "Well, Jerry, this new bill will allow-"

Mickey's growl rose in volume and pitch, growing more and more urgent as the man continued to talk. He had stopped thrashing his head back and forth, but his whole body continued vibrating and twitching at random as he stared at the screen, his loud angry growl rumbling on and on.

Beckett put her hand on Mickey's head and called his name again, but he didn't react, didn't relax his stance at all until the picture on the TV changed, now showing the news anchor again.

"Senator Bracken also told us that..."

"That's weird, right?" Castle asked in a hushed tone, fascinated. Beckett nodded, staring at Mickey.

"Very weird. I've never seen him do that bef-"

The picture on the TV changed again, the politician once again speaking, and Mickey went stiff again. His growl resumed. Now he turned his head, seizing Beckett's hand in his mouth and pulling it to the screen.

"Mickey, what the-"

As soon as her fingers touched the image of Senator Bracken on the screen, Mickey released her hand and gave several sharp barks, turning to look into her eyes.

Transfixed, Castle rose to his feet. His mouth was dry. "Beckett. Beckett, is he telling you something? Is he-"

"I think so," she breathed, gaping in shock at the dog.

On the screen, the news broadcast moved on to the weather forecast. All at once, as if a switch had been flipped, Mickey relaxed. He wagged his tail, gave Beckett's hand a lick, then lay down on his dog bed and gazed expectantly at both of them. The tremors seemed to be gone, no hint of the internal conflict he had been experiencing a moment ago.

Beckett turned to look at Castle, her eyes alight. "You saw that, right?"

"Yeah I did," he exclaimed. "He was showing you Senator Bracken. It was a message."

"And Coonan was fighting it, trying to keep Mickey from telling me. From telling me... that Bracken is the one who hired him to kill my mother," she breathed, tasting the words, feeling the truth of them.

"But why? We need-"

Mickey interrupted with a loud whine, drawing their attention to him. Castle startled when he saw the dog stretched out full-length, shivering. It looked like a lesser version of the convulsions he'd shown earlier, when Coonan was entering his body.

But this time it lasted only a moment, and then the dog stood up again, slowly this time. The difference was noticeable; Mickey seemed suddenly frail and unsteady on his feet, moving with care. Gingerly, he nudged his nose into Beckett's hand. She scratched his head and looked into his eyes.

"He's gone already." Amazed, she lifted her gaze to Castle again. "Coonan's spirit is gone. It never happened that fast."

"I guess he did what he needed to," Rick said. "He told you what you needed to know, even though he didn't want to." He nodded toward the TV. "Mickey found a way to help you get the name after all."

"Mickey helped me..." she repeated in amazement. "He..."

Their eyes met again as the same realization hit them both simultaneously.

"Wait a minute," Rick said with dawning excitement. "The demon's deal was that you were supposed to let Mickey help you. But all these years, all those spirits coming through him-"

"-that wasn't him helping me," she picked up the thread, her eyes wide as she pieced it together. "It was helping them."

"When he shows up at a crime scene, that's not him helping you either, it's the soul inside him doing it," Castle put in.

"But Coonan-" She let out a huff, shaking her head. "Coonan never would have told me who hired him to kill my mom. Even if he had lived, even if we had captured him again, no matter what bargain we'd tried to offer, he wouldn't have taken it."

"He was fighting Mickey the whole way. That's what that was, like you said." Rick looked down at the dog, who was once again lying on his bed, resting his chin on his paws. He was calm now, his big furry body relaxed and in control. "Coonan didn't want Mickey to tell you about Senator Bracken."

"But he couldn't stop him." She knelt on the floor, stroking the dog's head softly. "Mickey knew this was what I needed most. He's the one who decided to tell me." She knelt down and kissed the top of Mickey's head. "What a good boy."

"Kate," Castle exclaimed, "do you know what this means?"

She turned her head up toward him again, and he saw the fire in her eyes - he saw the witch.

"Yes," she confirmed. "It means I need to summon that demon again." Her lips curved upward, not with amusement but with menace. "And this time, he's going to have Hell to pay."

Thanks for reading and reviewing! The final chapter will be up tomorrow.