Based on the anonymous tumblr prompt (via castlefanficprompts):

4x20. Beckett goes out with Colin for that drink. Hours later after Hunt has left, Castle gets a call from his bartender at the Old Haunt, asking if he could come get Detective Beckett because she was too drunk to drive home.

"Casssle," Beckett drawls, slipping off of her barstool and struggling to stay on her feet.

He immediately slips an arm around her, his anger at her pushed aside by concern for her safety. "What happened, Nick?" Castle asked, looking to the bartender for help.

The kid's fresh out of college and still not used to the drunken patrons that frequent the city's bars, so it takes him a minute to find his voice. "She had a couple of drinks with some blonde guy… British, I think."

Castle grimaces.

Hunt.

The kid sighs, nervously wiping down the bar for what must have been the hundredth time since he called Castle. "Anyway, the guy had a plane to catch and she told him that she was fine to drive home." Nick eyes Beckett, who's currently leering at Castle as her hands wander. "That was about five shots ago."

"Why'd you let her keep drinking?" Castle asks, the words coming out much harsher than he'd intended.

"She's a hard person to say no to," Nick answers sheepishly.

Castle sighs and looks down at the semi-conscious woman in his arms. Regardless of what state she's in, it's never easy to refuse her. But in this moment she can barely keep her eyes open, let alone walk or drive, so Castle makes an executive decision and grabs her purse and coat. "You good to close up tonight?"

Nick nods and returns to his excessive countertop cleaning.

Castle balances Beckett's belongings in one arm and her body in the other, finally stopping to remove those damn heels as he helps her into his town car.

His driver doesn't question the pair, simply clicks on the Favorites section of his GPS and begins the drive to Beckett's apartment.

Beckett's head lolls to the side and she blinks up at Castle with those big, hazel orbs. When he doesn't say anything, simply looking out the opposite window, she reaches up – rather boldly, thanks in no small part to the alcohol – and turns his cheek so that he's facing her. "Why don't you look at me anymore?"

Her voice is too vulnerable to look away, but Castle can't bring himself to make eye contact either, so he settles on the Omega at her wrist. "I look at you."

She whimpers and maneuvers herself into a semi-straddle in his lap. Castle immediately tenses but can't make himself push her away. Her lithe body is too much to handle and he struggles enough just trying to suppress the shivers at the feeling of her chest flattened against his. "Not like you used to."

"Wha, what?" Castle stumbles over his own words for once in his life.

"You don't look at me like you used to." She dips her head to his chest, the vodka strong on her breath.

"Yeah, well – a lot has changed."

"Like what?" she asks, again whimpering.

"You know what I'm talking about, Beckett."

She sighs, "And it's always Beckett. Never Kate."

Beckett dips her head to his chest at that point, forehead meeting collarbone. The car swerves as she does so and her body goes to follow but Castle wraps his arms around her, keeping her from falling.

She begins to shake and soon enough Castle finds the shoulder she's leaning on is wet, damp with her despair. He does the only thing he can think of and cups her skull, stroking her back with the other hand. "Shh…"

"I'm so sorry, Castle. I'm so sorry." He doesn't say that it's okay – because it's not, and he can't add to the lying in their relationship – and simply holds her tighter. "Castle," she sighs, fingers skimming his ribs and resting so that they're cheek to cheek. "I don't know what I did wrong."

He freezes, realizing for the first time that Beckett might not know what he heard. "You could have just told me, Kate." She molds herself to him. "It would have saved us both a lot of misery."

Her cold nose finds it way to the skin of his neck. "You were supposed to wait for me."

"Wait for what? For you to tell me that you don't lo- that you don't feel the same way?" He barks out the last bit, harsher than he'd meant to for the second time that night. His driver glances back quickly, and Castle avoids meeting his curious gaze.

"Rick, please." Neither are quite sure what she's asking, but Castle continues stroking her hair. "Thank you," she murmurs a few blocks later. Castle can't decide if he's grateful or irritated that her apartment is so far away from the Old Haunt. "Thank you for taking me home." She shifts in his lap again, sniffling. "I know Nick could have just called a cab."

"Oh, Kate." He struggles to blink back any unwanted feelings. "You've ruined me for anyone else." He sighs; keeping his voice low, to the point that she feels more than hears his words. "If you don't know that by now, obviously we're doing something wrong." Castle notes that they've turned onto her street and is suddenly filled with a sense of dread, accompanied by adrenalin. Nostalgia maybe, if that's even possible. "I'm yours, Kate. If nothing else, just know that."

She sniffs against his chest as the car comes to a halt, and Castle holds his breath, equal parts frightened and proud of what he'd just shared. But when she doesn't move, Castle pulls her away from his body to find that she's fallen asleep.

Not knowing how long she'd been awake, or how much she'd remember once she sobered up, Castle lifted her out of the car and carried her to her building.

It wasn't until he'd fished Beckett's keys out of her bag and carried her to her bedroom that she stirred, reaching for him from her bed. "Mhmm, stay with me, Castle." He pauses, considering her request as he places a glass of water and two Ibuprofen at her bedside.

"Can't."

She sighs, rather adorable when she's flustered, but he can't be thinking that way. "Until tomorrow then?" She asks, settling into her bed as her eyes begin to drift closed again.

"'Night, Beckett."

Castle turns away before he can change his mind, heartbroken and still madly in love with her, before locking up and retreating to his town car.

It's not until they're well on their way to Broome Street that he thinks about dedicating the next few weeks solely to his book, avoiding the precinct until he can clear his head and give Frozen Heat the ending it deserves. Maybe he'll give Jameson Rook the ending he deserves, an ending.