I want you to have this.

Your place or mine? The question she hated hearing, the question she hated asking, was the mantra by which they were living. It didn't help that they rarely left together. She always had paperwork to finish, he had a family to take care of, which meant late night phone calls and empty beds.

Her favorite nights were when she got back late, after a draining case, finding him waiting by her door with flowers or a bottle of wine. But she always felt guilty, making him wait outside for her. He did just as much work as she did while he was with her, and had to be as weary as she was after a long day. Those were the nights they collapsed into bed with each other, barely making it through a full glass of wine before their exhaustion set it, finding comfort in each other's arms.

"Your place or mine?" He asked her one day, remaining a respectable distance away from her. If things went the way she wanted them to, his hand would be situated in the small of her back, them leaving together instead of at arm's length from one another. Except that, right now, would get people asking questions, questions they couldn't answer.

She brushed her hair behind her ear, meeting his baby blue eyes. "Mine, but a little later. I have to get a few things done. Can I call you when I'm all done?"

He grinned, his hand reaching out to grab hers before realizing what it was doing and returning his hand to his side. "Of course." He looked around, taking note of who was there and paying attention before turning his head back toward her, his eyebrows raising up and down, making her laugh. "See you tonight, Detective."

She rolled her eyes and shook her head, her grin plastered on her face. "See you tonight." She left him, finding her car quickly and climbing in. Billy Joel's Uptown Girl played on the radio, and she sang along at the top of her lungs the entire trip to the hardware store.

The machine was loud as it copied her key, the sound of metal grinding against metal sending shivers down her spine. She walked into the next aisle, away from the noise, and let herself look at the covers, something he could put on top of it to distinguish it. Her fingers landed on a simple blue cover before her eyes fell on the Iron Man rubber one. Her hand moved to that stack, searching through their characters before settling on Iron Man.

She left for the grocery store, his key tucked in her pocket. She only bought important things now, cream for their coffee in the mornings, eggs, chicken in case they actually made dinner at her place, as well as a few boxes of pasta. She called him from the car on the way home, him picking up after the second ring.

"You're not home yet."

Her mouth dropped open as she pressed on the gas pedal just a little bit harder. "You're waiting outside again, aren't you?"

"Well, Alexis was leaving to go to the library, and my Mother had some of her students over, rehearsing. I couldn't get much done."

She chuckled, hitting her blinker to turn into her parking garage. "Well, I'm just getting here, and I was calling to tell you to come on over whenever you were ready. I guess you were just ready earlier than I'd expected." She pulled into her place, gathering the bags in one hand from the passenger side as she made her way to the elevator. "Do you want to order something? I don't feel like cooking today."

"I can do that. See you in a bit." She ended the call, putting the phone back in her pocket and pulling out the new key. She carried it in her hand so he wouldn't see the cover, or that it wasn't attached to her keyring. But by the time she got to him, he was deep in conversation with the restaurant, stopping only long enough to take the bags from her hands as she let them in.

Once inside, she kicked off her heels as he started putting the groceries away, moving around her kitchen with the same ease that he moved around his own. She watched him from the island, her head resting in her elbow, a soft smile on her face. He hung up his phone, turning to meet her eye. "They'll be here in fifteen minutes."

"Good." She watched him put the last of the perishables away before tapping the seat next to her. "Can you come here for a sec?" His eyebrows knit together as he made his way to her, sitting and reaching his hand out towards her. She tried not to alarm him as she pulled her hand away. "We can't keep doing this." At his widened eyes she chuckled, shaking her head and finding his knee with her free hand. "Not this relationship, that's not what I mean."

She watched him deflate, relief flooding his features as he relaxed. "Good. Could you tell I was a little worried for a second?" His grin calmed her nerves, and she found herself leaning closer to him.

"Sorry, my fault. What I meant was, you can't keep waiting for me outside my door like that. I feel bad. And what happens if I pull an all nighter at the precinct, are you just gonna wait there all night?"

His eyes were concerned, and he caught her free hand in his. "I'm sorry. I'll wait for your call next time."

She shook her head, a smile playing across her features as her hair tickled her shoulders. "No, that's not what I want either. I want you to have this." Her hand unfurled, revealing the key in her palm. He looked like a kid at christmas, picking up the key and holding it delicately between his fingers.

"Iron Man? Kate,"

"I know, but they were out of Batman, and I figured Iron Man was next on the list for coolest toys." She interrupted, her arms crossing over her chest.

"No, I was going to say that I loved it." His eyes shone as he slipped the key into his pocket and leaned forward, his lips meeting hers in a soft kiss. They pulled apart so that their foreheads touched, each grinning, looking into the other's eyes. "Thank you."

She shrugged, getting up to put the rest of the groceries away. "It just seemed like the next logical step." She didn't go off on a tangent about how he was the only person in the world that she'd ever trusted enough with a key, or how she wasn't afraid of what he may find because he already knew everything. Sure, it was the next logical step, but it was so much more than just that. There was a knock on the door then, and Castle got up to get their food. And they collapsed into bed together that night, her head on his chest, listening to his breathing slow as she drifted off.

The next day, in the cardboard holder around her coffee, she found her own key to his loft, a blue cartoon elephant painted on the top part of it.

A/N: I'm not as crazy about this one as I am about the others, but I'm two days behind and I don't feel like fighting with this one any more...