Kate's fingers momentarily still over her keyboard as she looks down at the scrap of paper Castle has placed next to the steaming mug of coffee on her desk. One end of the little yellow post-it sticks up at her, and she sees Kate - Will you be my Valentine? written across the top. Two boxes are scrawled below that, with "yes" and "no" beside either one.
She purses her lips in an vain attempt not to smile and looks up at him as he settles into the chair next to her desk, shrugging off his coat with his face set in the picture of innocence. She arches an eyebrow and he continues the charade, smiling curiously.
"What?" He asks, and she rolls her eyes, picking up the mug and taking a sip before turning to him again.
"I think I might be a little old for you, Castle," she says as she puts the mug down over the post-it and resumes typing, eyes back to the computer screen. "I make it a point to try not to date fourth graders."
"You wound me, Detective," he responds, and she doesn't even have to look at him to know he has his hand over his heart in mock-offense. There's silence for a moment, until he leans an elbow on her desk and inserts himself into her line of vision again.
"You know, if you need me to extol my good virtues to help you decide-"
"We'd be here all day, and I'd never get any of this done," she cuts him off, but she's pursing her lips and smiling again as he harrumphs and leans back into the chair.
"Why are you here today, anyway?" She reaches for a pen from the edge of her desk, pulling a sheet out of a new folder from the top of the hefty-looking stack. "We don't have a new case, and I'm pretty sure you're not dying to help me do paperwork."
Castle shudders, confirming her suspicion, but then shrugs.
"It's Valentine's Day. Where else would I be?"
She inhales a little more sharply than usual and unconsciously holds her breath, her hand poised over the little box on the form that's awaiting her signature. Her head inclines the slightest bit towards him, but if Castle had noticed her reaction to his words, he's giving no indication; having picked up a red paperclip from her desk and gone to work prying it apart, he's distracted already.
Giving her head the briefest shake to clear her brain, Kate leans down over the form again, the slow smile only beginning when her face is hidden from view by brunette waves.
She startles a few minutes later when Castle jumps up from the chair, calling Esposito's name across the bullpen as he holds up the paperclip, now molded into the shape of what's presumably supposed to be a heart. She can't hear what Castle's saying as he makes it to her co-worker's desk, but the incredulously judgmental look on Esposito's face is enough to make her laugh. She goes for another sip of coffee, regarding the boys over her mug as she rests her elbows on her desk, her eyes eventually drifting down to the post-it still stuck on her desk.
It's not until much later that night when Castle is back at the door of his loft, stomach full of Chinese food and mind still lingering on the vision of a laughing Kate Beckett reaching across her desk and digging her chopsticks into his container of sweet and sour chicken. He sticks his hands into his coat pockets to dig out his keys and frowns slightly when his left hand brushes something unfamiliar, pulling out a crumpled piece of paper. Puzzled, he unfolds it, and his forehead creases disappear as he recognizes his own handwriting and someone else's solid checkmark placed in the box next to "yes."