He wants to erase every word of Heat Wave. Pull out the manuscript and cross out every sentence with black, thick lines. (He wants so desperately to save her.)

XXX

There's frustration catching in the back of Castle's throat, choking him, as he stands outside her apartment door and just stares. Somewhere between getting out of the cab and listening to the elevator doors slide shut he lost his courage, and he's trying to regain it, build it up again brick by brick.

Suddenly the door flies open, and Beckett's pointing a gun at him, and crap, sometimes he forgets how much she can scare him.

"Castle? What are you doing here?"

He swallows thickly, trying to remember how to breathe again. "Wine?" he asks, showing her the bottle in his hands and giving her a faltering smile because she's still kind of pointing a gun in his general direction.

Beckett half frowns at him, but there's something in her eyes that totally betrays the look on her face. "Fine, Castle. Come on in."

He flashes her a grin and brushes against her as he walks through the door. "Ah, Casa del Beckett," he says airily as he looks around, and he can already feel Beckett rolling her eyes behind him.

XXX

(Castle peeks in through her bedroom door just once, when he knows for sure she's asleep.

He stands there with the wine still buzzing through his veins and I'm not going to leave you alone still resting against his tongue, and he feels a little brave. But only until the sleeping form of Kate Beckett moves slightly. Then Castle practically sprints back to the couch and hides beneath a pillow.)

XXX

Tendrils of flame and smoke lick at the sky, and Castle is so very sure that his heart has stopped beating.

"Beckett?" Her name comes out stuck somewhere between a shout and a question. "Beckett!" He starts running toward the burning building, because he has to save her. (He promised to never leave her alone.)

XXX

Later, when they're both sitting in the back of an ambulance, still shaking from all the adrenaline, Beckett slides off his coat and places it gingerly in his lap. "Thank you, Castle," she says hoarsely, jumping slightly when his fingers find her elbow and tighten, keeping her from moving (running) away.

"Anytime, Beckett," he replies, and he tries to make it sound light, but it just comes out sounding tired. What he really wants to say is I'm so glad you didn't die, but he's pretty sure she already knows that. "So, now we have a killer to catch, for real this time," he says finally, and his voice still sounds so tired. He loosens his grip on her elbow and climbs out of the ambulance.

"We'll get him," she says confidently, and Castle turns to look at her.

"I know," he nods (but sometimes he wonders, and right now there's an overwhelming sense of doubt weighing him down).

XXX

When Castle returns to his apartment that night he hangs the dirty jacket up in his closet, knowing he'll never wear it again. The fabric smells like fire and it's totally covered in soot, but beneath all of that, he can still smell her. Cherries, soap, and something inherently Beckett.

(He keeps it as a reminder of what he almost lost.)

XXX

He says yes you do without a thought, because he can still taste smoke in the back of his mouth, and he hasn't really stopped shaking since he helped her out of the tub.

"Thank you, Castle, but I couldn't."

At this moment he doesn't care what she does or does not want to do, he just wants to know that she is safe. "You can and you will."

She shoots him a glare, and maybe once that would have scared him away, but not after all of this. (He can still remember the feel of her door under his palms as he knocked it down, can still feel the ash coating his tongue.)

Castle stands up and swings Montgomery's door open, holding it until Beckett finally rolls her eyes and exits the office.

"Beckett." She doesn't turn around, just keeps walking toward her desk to gather her things. "Kate," he hisses and follows after her, fists clenched.

Her head snaps up at the use of her first name, and her eyes narrow.

"I just want to know that you're safe for the night, that I don't need to worry about you being blown up by a serial killer again," he says, hand grasping onto the side of her desk tightly.

Beckett's knuckles are white as she grips her coat, and Castle takes a hasty step back from the desk, fingers dragging along the top of his chair. Her words are steady, but he can tell she's trying not to yell at him. "You don't need to protect me, Castle. We've already been through this."

"You need somebody to look after you."

"I don't," she says, and spins away from him, marching toward the elevator. Castle sidles up next to her just as the elevator doors slide open, and they step in together (always in sync).

"I'm sorry," he says softly, when the doors shut. "Sometimes I forget that you're this strong, very capable woman with a gun."

The corners of her mouth twitch upward. "How can you forget I have a gun when I'm constantly threatening you with it?"

Castle leans in toward her. "I'm probably traumatized, blocking it out."

Beckett rolls her eyes, but she's also smiling, so Castle grins back and nudges her shoulder. "It's true."

"Sure, Castle." She doesn't move away from him, and he counts that as a victory.

XXX

"Castle, you're my only backup."

He nods once, gripping the gun tightly in his hands. They can't die here, in a darkened warehouse, at the hands of a deranged serial killer. (It's not how he would write it.) "Beckett-" The words die in his throat, and she slips off into the dark to go save the world. Castle pauses for a moment, just breathing, and then follows behind slowly, hoping that Nikki Heat is as strong as he believes she is.

XXX

Castle goes home that night and tries to forget the feeling of cold steel in his hands.

Nothing works until his phone rings and he hears Beckett's voice on the other end of the line.