The homicide floor of the 12th Precinct was a busy place, detectives and officers alike greeting Castle when he stepped off the elevator before returning to their hushed conversations. The news of the victim's connection to him had spread quickly. Alexis was loved by everyone in homicide, and many offered Castle their condolences and asked him to pass them on to his daughter.

He spotted Kate in an instant. She was at the murder board, Paige's DMV photo already displayed, an almost empty timeline below. The only thing at the moment was the time of death; the neighbor hadn't known the exact time she'd gotten home, but it had been a little after nine in the morning.

Kate turned when he approached, and she grabbed his hand, pulled him into her office. "I'm so sorry," she said, shutting the door before turning to wrap her arms around his neck.. "Have you talked to Alexis yet?"

Castle sighed, his face buried in his wife's neck. His mind had raced nonstop on the drive from Paige's apartment to the precinct, but the feeling of Kate's arms around him and the subtle scent of her cherry shampoo grounded him, eased the dizzying rush of thoughts. "No, she didn't pick up. She's probably in class."

Kate pressed a kiss to the side of his neck and pulled away, fingers threading through the hair at his nape. "Are you okay?"

He lifted one shoulder. "I will be when we find the guilty bastard."

"About that." Kate sighed, then led him to sit on her couch, fingers lacing with his as she dropped onto the cushion next to him. "I know how you're going to react, but I have to say this. You shouldn't work the case, Rick. You're too-"

"Close?" Castle interrupted. He'd expected her to say that. "Like hell I shouldn't work it. I've known Paige since she was a little girl. She's Alexis's best friend. Was," he corrected himself. "I'm working it, Kate. You, of all people, should understand that."

Kate nodded and dropped her eyes to their hands clasped together on her lap. "I know, I'm sorry. I had to." She let go of his hand to brush her fingertips along his jaw. "Whatever you need, okay?"

Castle gave her a small smile. He leaned forward to catch her lips with his, to draw further reassurance from the soft touch. "Thank you. I love you, Kate."

"I love you, too. Keep me posted, okay? I'll help however I can. And Rick," she added when he stood, "be careful."

"Yeah, if you could send it right over. Thanks." Ryan hung up the phone when Castle emerged from Beckett's office and joined him at the murder board. "I just got off the phone with Columbia. They're sending over her schedule. Apparently, she was a TA for one of her professors. Espo's talking to him now."

Castle took a marker from Ryan's desk and added what he knew to the board. He hadn't seen Paige in several months, so he'd have to get some information from Alexis and Paige's parents.

Oh, her parents.

"Has her family been informed?" he asked.

Ryan jerked his head towards Beckett's closed door. "Beckett's trying to get a hold of them. Apparently, they're out of the country." He paused. "You alright, Castle?"

"Yeah." He finished writing Paige's major and turned to find Ryan, his brows furrowed with worry. "I'll be better once we solve this."

Esposito hung up the phone and stood, grabbing his coat and notepad. "That was the professor. He couldn't think of anyone Paige had a beef with, except one, who got upset at a bad grade."

Ryan shrugged. "Students get pissed at bad grades all the time, especially at an Ivy League school. What's so special about this one?"

Esposito glanced at his notebook. "Because this one called her, and I quote, 'a lying bitch who deserves everything bad that happens to her.'"

Ryan nodded at the new information, grabbed his coat. "Let's go. You coming, Castle?"

"Yeah." He followed them to the elevator, but his phone rang just as the doors opened. He looked at the screen to see Alexis's smiling face, his heart sinking at the image. "Never mind," he told the boys, turning towards the break room. He shut the break room door behind him before swiping to answer the call. "Hey, Pumpkin."

"Dad? What's wrong? Are you okay?"

Alexis sounded confused, and Castle didn't blame her. His message had been vague on purpose. He closed his eyes, hating that he had to tell his daughter that her life was forever changed. "I'm fine. But, uh, I need to talk to you about something. Where are you?"

Ryan and Esposito visited the potential suspect's dorm first, only to find out that he was probably in the main library. His roommate hadn't known Paige, or what had apparently happened.

The boys searched the library floor by floor, moving through the stacks quietly, but didn't find the suspect until they reached a study room on the third floor. Esposito motioned for Ryan to flank from the far side, and he approached quietly. "Steven Walker?"

Steven lifted his head from the book in front of him, turning to glance at the badge on Esposito's hip. "Can I help you?"

"Detective Esposito, NYPD. I need to ask you a few - hey!" he yelled when the young man bolted out of his chair, rushing through the library, darting between shelves of books. Espo cursed under his breath as he and Ryan pursued him, ignoring the protests from staff members and other students.

He burst out the front door only to see Ryan with the suspect in front of him, slapping handcuffs on his wrists.

Ryan grinned at his partner. "Been slacking on the exercise?"

Espo just shook his head and tried to catch his breath from the sprint down the stairs. "Shut up, man. Steven Walker, you're coming with us."

Walker was silent for the entire ride to the precinct, speaking for the first time to ask what they wanted when they put him in interrogation. Ryan and Esposito let him stew while they got an update from Beckett about the case and Paige's connection to the suspect. They had no physical evidence, only circumstantial, and not nearly enough to get a warrant to search his room.

They needed a confession.

"Steven Christopher Walker," Ryan boomed as he and Esposito dropped to their seats across from the suspect. "How do you know Paige Galloway?"

Walker looked between the two detectives. "What?"

Esposito leaned forward. "Why'd you run, Steven? Guilty people run. You guilty?"

"Whoa, hold on," Walker interrupted, holding his cuffed hands in front of him. "What's going on? Don't you need to read me my rights? Let me get a lawyer?"

"Why, do you need one?"

"Just tell us about your relationship with Paige," Ryan insisted. He leaned forward as well, mirroring his partner's pose.

"Look, whatever she said about me, it isn't true."

"What isn't true?"

"How do you know her, Steven?" asked Espo, voice raising with simmering anger.

"She's the TA in one of my classes," Steven explained. "She was, ah, helping me with my grade."

Esposito raised an eyebrow. "Then why'd you kill her?"

"I - what?" Steven just stared, eyes wide and glued to the crime scene pictures they laid out before him. His jaw dropped. "I didn't - you think this was me? I didn't do this!"

Ryan set a hand on Esposito's shoulder when he started to stand. "Why'd you run at the library?"

"I thought-" Steven sighed. "I had weed in my bag, man. I thought that's why you were coming after me."

Ryan shared a look with Esposito. "We don't care about the weed. Tell us about Paige."

"She's the TA in my Intro to Psych class. I was falling behind, and she offered to help, get my grade up. I had a paper due, and she claimed I'd plagiarized it, but she wouldn't tell anyone if I started sleeping with her." He dropped his forehead to his hands. "I did, but she gave me a C. I can't get a C, I have a scholarship."

He looked back up at the detectives, panic and worry in his eyes. "Look, man, I was pissed. I found her in the professor's office this morning and confronted her, sure."

"You said she deserved anything that happened to her," Ryan cut in.

"Yeah, but I meant a bad grade or something. We fought, she said too bad about my grade, I left. Went to the library, and I was there until you found me."

Ryan stood and nudged Esposito's arm. "Right, we'll see about that."

"Wait, hang on, one more thing," Steven called out as they opened the door. "I heard her on the phone when I got there. She said she'd see the Dean at 10 tomorrow morning. Maybe whatever that meeting was about got her killed."

"Right." Ryan followed Esposito to the murder board, where Beckett was already adding Steven's testimony. "I'll call the school, get surveillance."

"Make sure you ask about cameras inside the library," Beckett piped up. "I left a message for Paige's building manager for footage from the camera at the main door. If Walker's lying, we'll find out."

"We'll find out if he's telling the truth, too." Ryan pulled out his phone and typed out a text to Castle.

Suspect claims Paige blackmailed him after framing him for plagiarism. Can you see if Alexis knows anything?

Castle's response was immediate. On it.