Castle watches from his place at her desk as her conversation with Gates shifts into a steely argument. The captain left the blinds open after calling Beckett in a few minutes ago and he winces as he witnesses Beckett on the receiving end of a verbal blow, as he hears the muffled snap of a reprimand and sees his partner's face remain hardened but blank even as her eyes flash with hurt, anger, maybe even offense. He can't be sure from the sidelines.

It's the case, he knows that, they all do, but it doesn't make the task of watching more weight added to Kate's shoulders any easier.

Their killer has struck again, taking the life of another girl that is far too close to Alexis's age for his liking, slitting throats of young women and leaving their bodies to be found in tourist attractions across the city. They were called to the crime scene for the third victim yesterday morning and at this rate, the killer is set to strike again sometime in the next 24 hours.

Kate is running herself ragged, already hunched over her desk or stationed in front of the murder board each morning when he arrives, the stain of purple beneath her eyes growing darker with each passing day. She won't rest until they have the son of a bitch, until she finds justice for these three girls' families, but she's practically dead on her feet as it is.

He doesn't know how much more she can take.

Castle sits up in his seat beside her desk when he notices Gates dismiss her, curses himself for not using the time to refill the empty mug near her computer with a fresh serving of coffee, or maybe grab her lunch instead. He doesn't think he's seen her eat anything more than handful of almonds from the bowl on her desk today.

She doesn't meet his eye as she pulls out her chair, falling into her seat with a strained exhale, her jaw tight with frustration even while her eyes blaze with grim determination.

"You okay?"

"Fine," she mutters, jerking her desk drawer open, searching around for a pen that he relinquishes. Beckett huffs and accepts the writing tool, but only begins fidgeting with the object, a nervous habit he's positive she adopted from him over the years.

"What'd Gates say?"

"I don't want to talk about it," she sighs, propping her chin atop her knuckles. "I just want to find this guy."

"We will," Castle assures her without missing a beat. "He may have made it this far, but he's going to slip up, they always do, and we'll catch him when he does."

"How many more girls have to die before that happens?" Beckett grits out, finally lifting her eyes to meet his, letting him see the anguish swirling there, the desperation hiding in the murky shades of brown her irises have become. "Because I don't know how many more parents I can face, Castle. I don't know how to keep telling them-"

She bites her lip hard enough to bleach the tender flesh, tries to swallow back the unsteady exhale that's already slipped past her trembling lips, and Castle scoots in closer, finds her hand atop the scattered files cluttering her usually neat desk.

"We'll figure this out, Kate."

It's not enough, not something he can truly promise her despite how much he wishes he could, but it has her palm flipping for him, her fingers embracing the twine of his.

She sighs, but rests her gaze on their tangled hands, offering a gentle quirk of her lips before giving his fingers a squeeze and letting go.

"Thank you," she murmurs, fiddling again with the pen still in her other hand. "For always having something reassuring to say."

Pride and relief weave their way through the concern for her, the pressure from the case, and he grins in return, tries not to gaze back at her like the lovestruck idiot he actually is. But before he can formulate a response, the phone on her desk is ringing and dread consumes his insides once again.

"Beckett," she answers, clipped and professional, just like always, but her spine stiffens a second later, the tension striking like lightning. "What kind of game?"

Castle rises to his feet at that, but she's already snapping her fingers at Ryan and Esposito, gaining the boys' attention and making a signal with her hand for Ryan, requesting a trace.

"You've been keeping tabs on the investigation then?" she continues, her voice cool, neutral, but her knuckles are white around the phone, her knee bouncing beneath the desk, and he wishes she would put the call on speaker.

"Just a few more seconds," he hears Ryan mumbling, but his eyes are on her, trying to read between the strict lines of her face.

"How about you tell me why you're doing this first?" Beckett goads, her voice falling into that softer, more understanding tone she sometimes uses on suspects when she wants to coax them into confession. Not many can resist professing their sins to Kate Beckett, but by the frown that etches deeper into the tight line of her mouth, he has a feeling the person on the other line isn't ready to serve his penance.

"Got it."

"Just in time," Beckett mutters, slamming the phone back in its cradle. She's up a second later, snatching her coat and ready to stride for the elevator.

"Pinpointed the signal to Washington Square Park," Ryan informs them while he and Esposito both rise, snagging their own coats in preparation.

Castle holds his tongue while Beckett gives her commands, biding his time for when they reach the elevator.

"He said we would recognize him, be able to pick him out of a crowd, and that we should get there before he does something regrettable. So keep your eyes peeled as soon as you're on the scene and radio in when you're close."

"Got it, boss," Esposito nods, but Beckett's already striding for the elevator, Castle on her heels.

The doors slide closed and Castle remains silent for a moment, allows her the routine sweep of the badge on her hip and the gun at her side she often performs multiple times on the way to a takedown.

"What did he say to you? I heard you mention a game?"

Kate shakes her head, drops it back against the wall of the elevator as they descend. "He just asked if we were interested in playing a game, taking a gamble on his next victim's life. Spoke in riddles for most of it."

Cool beads of sweat form on the back of his neck, a familiar curl of terror coiling in his gut, because this feels too much like a case they worked nearly two years ago, when a serial killer became obsessed with her, blew up her apartment and almost took her life. Twice.

"It's not going to be like it was with Dunn, Castle," she murmurs, reading his mind all too easily and reaching out to find his hand, surprising him with the embrace of her fingers. Twice in one hour he's held her hand in his own, felt her slender fingers twined with his, and if they weren't on their way to confront a budding serial killer, he would consider this his lucky day. "It's just like you said, he'll slip up and maybe he just did by alerting us to his current whereabouts."

She squeezes his hand before the doors can shift open, before she releases it completely, and he exits the elevator at her side, matching her determined pace as they make their way out of the Twelfth and into her squad car.

He wants to agree, to believe in his own words from earlier, but this doesn't feel like an impending victory. This feels more like walking into a trap.

Washington Square Park is peaceful, swollen with people and the sounds of nature combined with the blare of the surrounding city. Winter is fading, slowly succumbing to the welcoming warmth of the approaching spring season, and Kate shivers at the gust of wind that ruffles her hair, slithers around her exposed neck, mingling with the anticipation bubbling beneath the surface of her skin.

Ryan is in communication with park officials, gaining access to the security cameras while Esposito works to round up a handful of plain clothes officers to block as many exits as possible, but for now, she and Castle are the only two on the scene.

"You said he claimed to have been watching us?" Castle murmurs, practically glued to her side as they come to a stop in the center of the park, right in front of the famous fountain.

"Can't tell how true it is," she mutters, scanning the area but seeing nothing out of the ordinary, beginning to worry that this is nothing more than a ruse constructed by some disturbed follower of the case or their killer's way of successfully throwing them off his trail.

"Loosen up, Beckett," Castle hums in her ear. "If he doesn't know what we look like, you'll give us away with the murderous look on your face."

Her lips quirk and he nods his approval, offering her a thumbs up, but she can tell he's nervous, feels the exact moment his anxiety spikes.

"Wait, I think I see him."

Kate follows Castle's gaze with a bored expression, sticking to their plan of remaining inconspicuous for as long as possible, and notices the man in all black, standing out amongst the sea of civilians in colorful winter wear. But it isn't the clothing that confirms Castle's suspicions, it's the tip of the blade peeking out from the sleeve of the man's sweatshirt, it's the turn of his head towards them, and the knowing look he gives her.

Kate lifts her fingers to the device hidden within her ear. "We've been made."

The man takes off and Castle bolts after him.

"Castle!" she shouts, already lurching forward to stop him, but he yells back to her over his shoulder.

"You go that way, we'll circle around, cut him off."

Her instincts flare with warning even as Castle's already dashing away in the opposite direction, reminder that she should not be allowing him such responsibility, especially when he isn't even armed, but they have no other choice. Esposito and Ryan are still five minutes away and she can't let this guy get away, can't let him take another life.

Beckett sprints through the crowd, keeping her eyes trained on the shadow of a figure weaving through the mass of people that fail to part quick enough for her. She's still too far away when she catches sight of Castle, racing towards the man with the determination of a bull, and their suspect must notice him too, must realize what sort of threat her partner could pose.

And that's when she sees the blade being put away in favor of a gun.

"Castle!" Her voice goes unheard, helpless to warn him, useless to stop the man who pulls the trigger.

A single shot fills the air, followed by the panicked screams of those around them, but she can't hear, can't see anything but Castle as he crumples to the ground, clutching his side with a hand that quickly becomes stained in blood.

The shooter is getting away, taking the opportunity to sprint towards the exit, and she needs to follow, she could still catch him, but her heart is like lead in her chest, her entire body paralyzed for a second too long, torn between the job and the man bleeding out on concrete, the man who loves her.

No matter what she chooses, she'll lose either way, but she still chooses him.