This one is A.) blatantly gratuitous, B.) ridiculous, and C.) roughly 50% stolen from an adorable scene with Goren and Eames in an episode of CI. So you've been warned.

Chapter 4: 1x02, Nanny McDead

Do I have to wait for him to sign, or can I shoot him now?

Castle doesn't even have words to describe how happy he is that he and Beckett wear the same color shirt the first day he starts shadowing her. If that's not fate, he doesn't know what is.

And he likes that they get to go to the park the next day. It's welcoming. Yet also unpredictable enough that he hopes something exciting might happen. Or maybe that she'll let him go on the monkey bars.

She seems fascinated by his marital record. Interesting.

"Exactly how many times have you been married, Castle?"

"Twice."

"That's it?"

What was she expecting, a closet full of spare wives? "Isn't that enough?" But now, back to his favorite new pastime: prying into her personal life. "How about you?"

"Me? No. Never been."

"Really?"

"Yep."

"You'd be good at it. You're both controlling and disapproving. You should really try it." On the other hand, he's willing to bet Mr. Kate Beckett is going to be a very, very happy man on the wedding night when the bathroom door opens and she steps out in sexy black lingerie, all smokey eyes and teasing lips and silky skin and those long legs and black lace that barely covers –

Whoa. Down, boy. He already asked her out. She already said 'no.'

They pause as they reach the metal fence near the play area so she can scan the crowd and he can scan her. "I'm not an if-at-first-you-don't-succeed kind of a girl, Castle. When it comes to marriage, I'm more of a one-and-done type."

God, she is cute. And hot. And trying really hard not to let him get to her.

So he fixes her with a too-intimate gaze that can't possibly be construed as anything but interest, because he's noticed it makes her uncomfortable and for some reason he's really, really enjoying it.

"Any serious candidates?"

She glances back at him, and he watches, delighted, as her cheeks flush a little and her mouth opens but nothing comes out. She is adorable when she's flustered.

But she covers it by looking back at the playground, scanning. "There's no one in a red vest. Do you think she's here?"

"Not a clue." He's still staring at her, because police legwork is her thing anyway. He's having lots of fun staring at her until she blushes. This might become his new favorite pastime.

She bites her lip (he loves when she does that) and lets out a frustrated breath. "I can't tell. Maybe someone around here knows who she is. We could ask the other nannies or moms."

"Ooh, not such a safe idea. Do you know how overbearingly protective Park Avenue mothers are? You can't just stroll in and start asking questions. They'll clam up."

He's mostly making this up – there are some very pushy mothers, but a female cop with a proper badge wouldn't make them nearly as nervous as he's pretending it would – but Beckett didn't grow up on Park Avenue and it actually seems like she believes him.

(Besides, didn't she say cops are allowed to lie? He's just trying to more closely imitate his muse.)

She lets out a sigh, shoving her hands in her pockets. "What do you suggest then, Sherlock?"

He puts on his most effective innocent expression, because he watched an episode of Law & Order once where the detectives were at a playground so yes, he has an idea and he wants to see if it really works.

She grudgingly admits that his idea might work.

So they find a prime example of Park Avenue Mom sitting on a bench and head over. "Excuse me, are these seats taken?"

She looks up, but smiles. "Not at all." Fake blonde hair, tastefully understated Burberry coat, khakis, Prada scarf. Yep. "I don't think I've seen you here before. Are you new?"

"Just moved here from Chicago. I'm Richard, this is Katie."

"Nice to meet you. I'm Evelyn." She fishes a tube of lip balm out of a purse that costs more than the GDP of small nations. "This is a wonderful park, by the way. Great place to bring kids."

Castle's happy they're finally doing real undercover work – though he'd be happier if there were wires and costumes and maybe fake noses involved – but he decides they need to look more like a couple. He reaches for Beckett's hand. She bats his hand away and shoots him a glare. OK. Maybe not. He settles for sliding it subtly on her knee before she can stop him. She immediately presses hers on top of it. It's not a gesture of affection. She's making sure it doesn't start wandering.

OK, so that plan won't work.

"Which one is yours?" beams Ballet/French/Viola/Art Class Mom.

Castle flashes her his warmest please-buy-my-books smile. "Little boy over there by the monkey bars – " there are about a dozen kids by the monkey bars – "he just turned four. Just started violin and beginning French class, too. Gonna be just as smart as his mother."

He squeezes her knee and beams at her, earning her fingernails digging into his hand, and he hides the grin, because Beckett is so uncomfortable right now but it's just too much fun and besides, it serves her right for trying to ditch him with the police legal rep yesterday. Even though he knows she's going to maim him for this later.

"Oh, that's so wonderful. My little twins are over there, Autumn and Lace." She points at two identical little pasty brown-haired girls in tiny designer jackets.

"They're very cute," Beckett offers. First time she's spoken up since he turned her into the third Mrs. Castle. At least it's not a death threat.

"They sure are." More. She hates him right now. "I keep telling Katie, I'd love for us to have a little girl. Someone I can really spoil. And we're definitely trying for one." He waggles his eyebrows, feeling Beckett's nails pierce his skin again. She is going to torture, then kill him.

Mother Park Avenue smiles sagely. "Well, I'm sure you'll get one. And I have to say, you've kept your figure incredibly well, Katie. What's your secret?"

Beckett gives her a tight smile. "Lot of working out."

Castle chuckles and manages to slip an arm around her shoulders before she can stop him. "My Katie is a real beauty, isn't she?"

He looks back at the playground, swarming with enough kids that he doesn't have to pretend any particular one is theirs. "Derrick! Derrick, play nice with the other kids!"

Beckett flashes him a look which is close enough to loving to satisfy Mrs. Khakis 'N' Pearls but which he can already tell means You named our fictional child after you own damn character, you asshole?

Ah. There's the reaction he wants: barely-bridled hatred. It's adorable. He wonders how far he can push her before she snaps and shoots him.

So he forces his fingers through hers, till their palms are laced together and she's glaring at him again and she really needs to calm down because really, they're just holding hands. It's not like he's trying to convince her to actually start making Derrick Batman Castle with him, after all. (The name is not negotiable.)

Not that he wouldn't be open to the idea. She's hot. And she's smart, and funny, and the way she bites her lip, and the line of her throat, just begging for him to –

Right. Case. Work. Information. And making sure she doesn't rip his hand off. She's trying to. He can feel her fingers moving. Think again, Beckett. His other arm is still around her shoulder. She's tense. She doesn't like it. "You know, Katie and I have been thinking about getting a part-time nanny for Derrick. Do you know where to look? We thought maybe we could talk to families who've had luck finding good ones."

Mrs. Burberry is happy to oblige, and within minutes they've asked about Chloe. Apparently she's a wonderful nanny, good with little Becca, and she's not looking for work right now but she knows several other young women who might be available.

"It's a little early, but she'll probably be out in a few minutes. I'm sure you can talk to her then."

"Great. Thanks." Beckett's finally managed to pry his fingers out from hers, and is now trying to get his hand off her shoulder.

"Of course. I tell you, they are such a godsend. My husband and I have a nanny who comes in a few days a week. It's just given us so much more time to be together."

"Exactly! That's what I've been telling Katie." Castle beams at Beckett, whose tight smile in response tells him she is already trying to decide where to dump his body. He ignores it, leans in to kiss her cheek lightly, feeling her tense immediately. "I want to be able to take time to really focus on her."

Beckett looks up at him with a look that tells him she's now decided where to dump his body. And since her face is right there and he's unreasonably attracted to her and he's going to die anyway, he figures what the hell? and pulls her closer to kiss her lightly on the lips.

She freezes, but it's over so quickly she can't do anything to stop him. He turns back to Mrs. Richie Rich, who's beaming at what she obviously thinks is an outburst of husbandly love, not a gamble on his life with a woman who's armed. "That's so sweet. How long have you two been married?"

"Sixr years in May."

"Adorable. And your son is a darling." Castle has to hide a smile, because she obviously has no idea which kid is Derrick Batman. "Well, if you'll excuse me, I have to get Autumn and Lace off to their harp lessons." Mrs. Fifth Avenue Cardigan smiles, clutching her purse. "Best of luck to both of you!"

"Thanks so much!" Castle waves, finally taking his arm off Beckett's shoulders.

As the woman leaves, Castle takes a deep breath, and sure enough, he feels Beckett's fingernails digging into his arm even through his wool coat. Um, yeah. She's not happy.

Kissing her might not have been the best choice.

She silently drags him away from the playground, back to the sidewalk, and she she lets him go, turning to face him. Her face is like ice. She is pissed.

And it's not like she's going to let him live anyway, so he goes for lighthearted. "Was it good for you? Because it was good for me."

Before he realizes what she's doing, she slaps him, her hand hitting his cheek with just enough force to actually hurt. He yelps, grabs his cheek. "Owwww! Beckett! What was that for?"

"What the hell is wrong with you?" she hisses at him, eyes shooting sparks. Maybe they won't be making Derrick anytime soon. "That was completely over the line!"

"Calm down, Detective. It was just a little kiss." No tongue, either, which is too bad. She has a pretty mouth. And he thinks she probably has a nice tongue. So it's really only like half a kiss anyway.

She grits her teeth. "You can not just kiss me in public for no reason, Castle!"

"We were supposed to be a couple! It was acting!" She sighs, and he can't resist. "Or maybe you're worried. Maybe you enjoyed it too much."

She huffs out a laugh, clipped and short. "In your dreams, Castle."

"Don't fight the feeling."

"Shut up."

"Just because you liked it – "

"Shut up."

"It's okay to say you liked it."

He sees her eyes narrow, and before he can respond to it she grabs his scarf, yanks him closer, pulls her face to his and kisses him soundly.

A muffled noise of shock escapes him (because what the hell?) but she's adamant, one hand on his neck holding him there. And then her tongue is in his mouth, warm and wet and she tastes like coffee and hotness and anger and good. She nips at his bottom lip and he groans. Shit.

Her tongue presses into his one last time before she pushes him back. He actually stumbles a little. Falls back on his heels. Like a hopeless teenager. And immediately needs her tongue in his mouth again. Right now.

"I said shut up, Castle."

With that she turns back to the playground. He stares. Did she – did that –

"Red vest. That might be our girl."

Beckett goes to follow the nanny who's just come into view, leaving Castle to stare after her for the moment it takes his brain to start functioning again.

Kate Beckett can shut him up anytime she wants.

And he was right. She does have a nice tongue.