*So, yeah, my brain is evil. And this is what it came up with when I heard the phrases "zombie apocalypse" and "otp". Fair warning, I cried *a lot* while writing this.

Disclaimer: I do not own Castle...obviously...

(Castle)

Castle stood guard at the safe house door, ushering their little band of survivors inside, his gun trained on unseen targets. Once everyone was through the door, he ducked inside, slamming the door shut and throwing the deadbolts.

A light flickered on and Castle scanned the room, doing a quick head-count. Kate, Chloe, Alexis, Jim, Gates, Esposito, Lanie, Jenny, and Thomas, Ryan and Jenny's little boy. Everyone accounted for. His mother had been killed almost two weeks prior, devoured by the first wave of zombies that had reached Manhattan. Ryan's loss was more recent; only two days ago. Thomas still didn't understand where his daddy was.

"Is everyone alright?" Castle asked, receiving nods and murmurs from the group. Somehow, he'd been appointed their leader, his years of playacting "zombie apocalypse" apparently making him the most levelheaded in this situation. Even Kate had insisted he take control, still shaken to the core by the fact that this was actually real.

Castle sighed, sinking down against the wall. Kate cuddled up beside him, her head dropping onto his shoulder. Chloe, their six year old daughter, crawled into his lap. The room grew quiet as everyone dozed, safe for the time being.

His eyes were just starting to close when Chloe shifted in his lap and said, "Mommy, your arm's bleeding."

Castle felt Kate shift away from him to check and then felt her desert his side completely a panicked "Fuck!" breaking the silence before she could stop it.

All eyes snapped to Kate, who was now standing in the farthest corner of the room, a hand clamped over her mouth and tears welling up in her eyes. Nobody had to ask what was wrong. The bite mark stood out, bloody and oozing on her forearm. She closed her eyes, let her hands drop, and whispered, "Kill me. Now."

An uproar broke out at her words, the loudest protests coming from Lanie and Alexis. "You have to do it," Kate insisted. "I'm infected. It's only a matter of time before..." Castle could see the words stick in her throat, but she stiffened her resolve and continued. "Sir," she said, turning to Gates. "Shoot me. Please."

Gates shook her head, horror written all over her face. "I...I can't," she whispered. "I'm sorry. I can't."

Kate turned her eyes on Esposito, who met her gaze reluctantly. "Javi. Javi, please," she begged, her voice breaking.

Espo didn't answer, merely dropped his gaze and shook his head.

"Come on!" Kate screamed. "You saw what those things did to Ryan. Your partner. Your best friend. They tore him apart, Javi," she said, her voice dropping to a whisper. "And I'm gonna be one of 'em if somebody doesn't do something about it."

Espo stayed silent. Castle's gut clenched as Kate turned to her father, desperation shining in her eyes. "Daddy," she whispered. "Daddy, please..."

Jim blanched. "Katie, don't..." He choked on his words, tears slipping down his face. "Katie, think about what you're asking me to do." He turned to Lanie. "There's a way to fix this, isn't there? She doesn't have to die."

Castle closed his eyes, taking a deep breath before standing slowly. "No, she's right," he said, unable to keep his voice steady. All eyes turned to him, Kate's included. "I'll do it."

A tear slipped down her cheek. "Thank you," she whispered, coming back to him and squeezing his hand. Her eyes flickered to his gun then back up to him. "Not here."

He shook his head. "No," he agreed. "Outside. Say your goodbyes," he told her, releasing her hand. "I'll be waiting."

Castle stepped out into the darkness, the oppressive heat making it hard for him to breathe. Or maybe it was the fact that he now had to kill the love of his life.

He heard the door open and close, and Kate was in front of him all too soon. "That was quick," he commented.

She shrugged. "I don't like long goodbyes," she said, her voice surprisingly steady.

"Can I..." Castle paused to catch his breath. "Can I kiss you?"

Kate shook her head. "Not a good idea," she said. "We don't know all the ways that this spreads, and..." She took a shaky breath. "And they need you."

Castle nodded, tears finally starting to fall. He held out his hand to her. She took it, smiling sadly. "In that case," he started, "this is me, kissing you for the last time, wishing there was something, anything, I could do to not have to say goodbye to you."

Kate hiccuped a sob, stroking her thumb along his skin. "And this is me, kissing you back, resisting the urge to devour your fantastically juicy brain."

Castle let out a surprised laugh. "Kate..."

She broke their "kiss," stepping back a few paces. "Do it, Castle."

He took his gun from its holster, clicked the safety off, and held it up, pressing the muzzle against her skin. Her eyes closed, and she took a breath, preparing for the shot.

It never came. Castle stared at Kate for a few moments before lowering the gun and dropping his head. "I can't do it, Kate," he confessed. "I can't hurt you. I can't kill you."

She nodded, wrapping her fingers around the gun he still held. "Then let me do it." He relinquished the weapon, grazing her knuckles with his fingertips.

"You don't have to watch," she told him. He nodded, turning around as she put the gun to her temple. He waited only a moment before the shot rang out and he heard her body hit the ground.

Castle took a breath and turned around. Kate was crumpled on the ground, blood staining the dirt, the gun still held limply in her hand. He knelt down, checking for a pulse. Nothing. He pressed a kiss to her forehead.

"I love you, Kate," he whispered. "Always."