It wasn't easy in the waning hours of the evening, but Hayley managed to spot the professor as he left his building. She'd been watching the apartment since she'd traced his phone there, and had called the boys when it had seemed like he'd be staying for awhile. They had questioned him with Hayley listening on speakerphone, but he revealed no answers.

The plan had been simple: the boys would talk to Birch, pretend they didn't know anything about his relationship with Paige. But over the course of the twenty-minute conversation, they steered it to how Paige had been killed or any potential motives. Eventually, Birch had clammed up and had all but forced the detectives to leave.

So they'd kept on the apartment since, just watching, waiting.

Birch stepped onto the sidewalk, gaze darting across his surroundings and presumably searching for anyone watching him, before he took a right turn. He obviously didn't notice Hayley, because he walked down the sidewalk at a fast clip.

Hayley sent a short text to Espo to let him know she was on the move; the boys were covering the back and side of the building. She kept several steps behind Birch as he turned one corner, then another, consistently letting the boys know where she was going.

The evening crowd was starting to thin, so Hayley had to be more careful, but as she turned yet another corner, she froze when she saw Birch step into an alley. Before she could sneak to the alley entrance, though, a swarm of police cars pulled up, sirens blazing, trapping Birch in the alley.

Hayley watched with a smile as Birch was arrested and placed in the back of a police car.

Beckett didn't waste any time. She strode into interrogation with confidence and two evidence bags and sat down, eyes on Birch.

She'd seen suspects of all shapes and sizes, had seen more reactions than she could count. But rare was the time she could interrogate someone who she knew was the killer. Even more rare were times when the killer knew they were caught and while she enjoyed the cat-and-mouse game of getting a suspect to confess, she was looking forward to pressing charges against this man.

"Why'd you kill Paige?" Kate asked, not wasting any time.

"I-" When Kate just raised an eyebrow and showed him the bag containing the murder weapon, Birch's shoulders slumped. "I didn't plan it," he admitted.

"Just tell me what happened."

Birch sighed. "I've been trying to get published for years, with no luck. If I don't get tenure I might lose my job, so I got desperate. Started to copy parts of papers, found that other people's words were better than mine. Paige found out last year and threatened to out me. But I couldn't let her, I have a family to support. I thought I could buy enough time to make it work."

He clasped his hands together, fingers playing with his wedding ring. "So, she blackmailed me. My money for her silence. And God help me, I paid her."

"What changed?"

"She got reckless," he said. "She started waving the money around, and her grades started to fall. She even had a fling with one of my students. So, today I went to her apartment to try to get her to stop, because I was afraid I'd be found out. People would start asking questions. We argued, she told me to leave, but I couldn't. I threatened to stop paying her, she said she'd out me."

Kate lifted the bags, one containing the knife, the other a bloodied navy sweatshirt that CSU had found in his laundry hamper. "We matched the knife with the stab wounds in Paige's body," she explained, "and when the DNA comes back it'll be a match with her as well."

"I didn't go there to kill her," Birch muttered. "But she turned away, and I saw the knife. I was just so mad…"

He trailed off, and Kate collected the evidence and opened the door. "It's over, Birch. You're done."

"Are you serious?" Alexis asked as Kate opened the door. She stood, wiping her hands on her slacks. "Professor Birch really killed her?"

"Yeah. We have the murder weapon, solid evidence, and his confession. You're free to go, no charges."

"Thank you." Alexis gave Kate a tight hug, eyes brimming with tears. "For everything."

Kate squeezed her before giving way to Castle, who practically pushed her aside to get to his daughter. "I'd say anytime, but I don't want any more family members accused of murder."

Alexis couldn't stop the chuckle as she pulled away from her dad. "I'm with you on that."

"You ready to get out of here?"

"Um, give me a sec?" She waited until Kate led her dad away, a knowing smirk on her face, and walked up to Officer Hernandez. He'd been on duty the entire afternoon, had made the time she'd been alone bearable. "Thanks, Officer."

"Kyle," he interrupted, accepting Alexis's outstretched hand. "It was my pleasure. I'm sure I'll see you around."

Alexis grinned. "Yeah, I'm sure you will." She hesitated before giving him another nod and turning away. "See you later, Kyle."

She found Ryan and Esposito in the bullpen, closing up the evidence box. The murder board was empty, presumably taken down when the DA had tried to have the case transferred. Both of the detectives greeted her with hugs, expressed their gratitude that she was okay, and most importantly, free.

"I know you guys took a huge risk by helping me," she said, "and I am so, so grateful for that. Thank you."

Ryan lifted a shoulder in a shrug. "It was nothing, Alexis. It's what we do for family."

Kate sighed as she and Rick walked through the door, and she used his shoulder as leverage to take off her heels. She was exhausted; all she wanted to do was collapse on the couch with a glass of wine and curl up next to her husband. The curling up she could do, but she dropped her head to his shoulder when she remembered that wine was off the table for the foreseeable future.

"You okay?" Castle asked, his arm curling at her waist, fingers drifting just below her rib cage, his lips at her temple.

Kate nodded against his shoulder. "I want wine," she complained.

Castle chuckled and nudged her head up, cupped her cheeks so he could kiss her softly. "I know. I can make you tea instead?"

"Yes please." She followed him into the kitchen and watched as he retrieved a wine glass, paused, and put it back. "You can have wine, babe. I won't hate you for it."

"It's alright." He put the kettle on, then joined her at the island. "Thank you," he said quietly, reaching over to take her hand and lace their fingers together.

Kate's thumb circled over the skin of his hand. "For what?"

"For what you did today. Being you." He tucked a lock of hair behind her ear, hand lingering at her jaw, and gave her a soft smile. "You'll be a great mom, you know. You already are."

Kate smiled and leaned forward to kiss him, her tongue swiping at his bottom lip. "I love you," she whispered against his mouth when she pulled away.

Castle smiled. "I love you, too."

Alexis was alone in her apartment, a glass of wine on the coffee table next to a photo album. The album was of her and Paige, pictures from their lifelong friendship. Kate had invited her over, but she'd just wanted to go home. Her dad would have been all over her, almost suffocating, and she needed space.

She swiped at her cheeks when there was a knock on the door, rushing over to answer it, and was surprised to see Hayley through the peephole. She sighed before opening it. "What's going on?"

Hayley lifted the pizza and beer in her hands. "Thought you might want some company."

"I appreciate it, but honestly, I'd rather be alone." Alexis wiped fresh tears from her cheeks, then stepped aside to let Hayley in. "No, I don't," she admitted.

Hayley joined her on the couch after grabbing plates and a bottle opener. "Aw, look at you two!" she said with a smile, pointing at a picture of a young Alexis and Paige.

Alexis chuckled through her tears, her fingers touching the edges of the picture. "We were eight," she explained, the memories of her friendship overwhelming her. "We begged Dad to take us ice skating, but the rink was closed and we didn't want to deal with Rockefeller. Instead, we went to Central Park and had a snowball fight, Paige and me against him. We killed him, of course-" She froze at her choice of words.

"I can't believe she's gone," she admitted, shaking her head. "I'll never see her again. Never get another text, or phone call, run into her in the library…"

Hayley rested her hand on Alexis's back. "You know, I've lost a few friends. And one thing I've learned is that if you focus on the good memories rather than the bad, it will start to hurt less."

Alexis nodded. "Thanks, Hayley."

"Anytime." She paused, allowed Alexis a moment to quell the sadness before speaking again. "Now, I have to know about this picture. Please tell me you're wearing that because it was Halloween."

Episode beta work by ivyandtwines and amtepe

Castle Season 9 is produced by Team Planet and the writing team of Castle Season 9. Executive Producer is encantadaa.

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