I have no beta for this story, so all mistakes are mine.

He brings her coffee. It's their thing. It began, she is sure, as a way to get on her good side. He tried with the machine in the break room first, but that was for everyone. The white cup with its brown collar, that contains her perfect latte is just for her. She knows the coffee started as a way to make his presence more tolerable and sometimes he used it as a peace offering. Mostly, it was their greeting.

Recently, however, coffee had morphed into something much more important. Since Kate had returned to the precinct, it had come to symbolize his promise, unspoken of course, to wait for her. The cup was a tactile reminder that he would keep showing up until she was ready for more than just a casual brush of fingers during the morning's hand off. Every day he brought her a cup of coffee, and every day she was reminded that he was there, waiting for her walls to come down.

More than once over the course of their partnership Kate had considered asking Castle for the source of his latte brilliance. She often wondered where she could find the place that seemed to make her beloved jolt of caffeine perfect every single time. Some mornings she would like to shake the hand of the barista who instinctively knew she would need a little something extra and would sneak in an extra shot of espresso. She imagined it to be a cozy place with huge, overstuffed chairs and low music playing. The kind of place where she could disappear for the afternoon and no one would bother her.

If she was honest with herself, as she was learning to be more and more lately, she desperately wanted it to be a place she could disappear to with Castle and no one would know where to look for them. However, despite her curiosity, Kate resolved to let the mystical land of perfect lattes stay a secret until Castle decided to take her there. She wanted it to be his decision to reveal the source of his magic and her work with Dr. Burke was helping her get ready for that day.

She felt more ready than ever the day she found herself clutching his hand through the encore performance of his mother's one woman show. Her two glasses of champagne made her feel light, a little giddy. The last cup of coffee before leaving work made her feel wide awake. That's how she found herself in Castle's kitchen, at midnight, helping him wash the delicate flutes. She'd waved an exhausted Martha and Alexis off to bed over protests that she didn't need to help clean up, she was a guest. Castle was smart enough not to argue with her and simply asked if she would like to wash or dry.

The pair worked in comfortable silence, Kate passing Castle glass after delicate glass until he was finally drying the last one. Kate wiped her hands on a towel and stepped around him. "Where do these go?" She asked, picking up a dried flute and stepping toward where he kept the other glasses.

"Not there. Those are the every day glasses. Leave it to Mother to use the cut crystal. Hence the hand washing." He pointed to a cabinet above his space age coffee machine. "They go in that one. Top shelf."

Kate pivoted and opened the door he'd indicated. There, on the top shelf were four more glasses like she one she was holding. On the bottom shelf, however, eye level with Kate, were four white plastic cups, a stack of lids and brown collars piled neatly next to them.

"Hey Castle, what are these?" Kate asked, her voice laced with confusion.

When Castle saw what she was pointing to, he was grateful her back was still turned and she couldn't see the widening of his eyes. He recovered quickly and replied, "You of all people should recognize a coffee cup when you see one, Beckett." She turned to face him as he continued, "Honestly, you call yourself a detective."

She leveled him with a glare and took a small step toward him. "I'm serious, Castle. Why do you have a stack of our cups in your kitchen?"

Castle responded by taking another step forward and reaching behind the canister where he kept his coffee beans. He didn't say a word, just pulled out a small bottle of expensive looking sugar free vanilla. Kate's breath caught in her chest as she put the pieces together. Tearing her eyes away from the little bottle, she raised her eyes to meet his. He was staring at her with a mixture of trepidation and overwhelming love. It occurred to her briefly that the discovery of these cups should not have sparked such a reaction in her, in either of them really. But then again, coffee isn't just coffee for them.

Kate was pulled from her thoughts on everything coffee means by the realization that Castle was talking.

"… and no where was open, let alone..."

"Wait," Kate interrupted, "start from the beginning, please. I missed that."

"The very beginning or…?" he asked, smiling slightly.

"Castle." Kate cut in again.

"Right. Okay. From the beginning." Castle took a deep breath. "When I realized you didn't get along well with the machine I got for the precinct, I decided I would bring you coffee. It started as a way to win brownie points or make my presence more tolerable and sometimes it worked."

Kate chuckled at this admission. Apparently their shared brain thing extended to their thoughts on lattes.

"Eventually," he continued, "I realized I had set a dangerous precedent without having an infallible source for all your caffeine needs. For the first two years, I took what I could get, whatever was open for a 3AM crime scene. Luckily, your order isn't complicated, but still, none of it was perfect." He paused here and took a deep breath. Kate thought it looked like he was steeling himself before he continued. "Then, last summer, when you were gone, Alexis took me to a coffee tasting room to try and cheer me up."

Kate knew now why he needed to pause. She also noticed he was careful not to mention the reason they'd been apart last summer. In attempt to reassure him that she understood, she reached across the island and took his hand, holding it more gently, with more reverence than she had during the show.

Castle seemed to draw strength from this gesture and carried on, "They had coffee from all over the world. It was incredible, but there was this one blend, from Brazil. I'd never had anything like it. It was strong, with a serious kick to it. But it also had notes of chocolate that gave it an underlying sweetness. It reminded me so much of you, although that's not remarkable. Last summer, everything reminded me of you." He met her eyes with a small smile and, once again, she could see the pain she caused him.

Kate's heart broke for him in that moment. She had many sins to atone for with this wonderful man, but now was not the time. Instead, she gave his hand a squeeze.

"Go on." She urged.

"I bought out their whole stock." he said in a whisper. "I drank it all summer. I guess it made me feel closer to you. I don't know." He shrugged. "When you came back, I decided I would take over making your coffee before I came to meet you. Honestly, I don't know why the thought never occurred to me before." He smiled at her and she returned it.

"Thank you for telling me that. I had no idea, but it's really sweet."

"It's just coffee." Castle said with a shrug, looking back down at their hands.

"It's not." Kate implored, inclining her head to meet his eyes. "It's a lot more than 'just coffee' to me and, unless I am mistaken, it is to you too."

"You're not mistaken." He murmured, holding her gaze.

"Good." she whispered, and leaned in to brush her lips against his cheek. "It's late," she said, finally taking her hand away from his and moving toward the door. "I should get home."

Castle followed her to the door and helped her into her coat.

Halfway down the hall, she turned at his voice. "Until tomorrow, Detective?"

Kate smiled. "Until coffee, Castle." And with that, she turned and made her way to the elevator.

On her way home, Kate reflected on this new layer he added to their story tonight. Castle loved her. She knew that. Bringing her coffee was a nice gesture. Knowing he took the time to pick out a blend of beans that reminded him of her and took the time to make her latte himself, no matter the time of day or night, was so much more. It reminded her of how much she loved him too. It reassured her that the work she was putting in would be worth it in the end. Tonight as it had so many times before, coffee acted as a wrecking ball. The walls around her heart were coming down and she could see Castle on the other side.

It wasn't until two weeks later, when she was tearing down the precinct stairs, desperate to find Castle, that she realized a warm cup of coffee on her desk could bring with it destruction of an entirely different kind.

A/N: I love writing about season 4. I hope this doesn't feel too outside cannon to anyone. I never gave the coffee much thought beyond realizing it was about more than just caffeine. But, the more I thought about it, the more it seemed strange that Castle could deliver perfect coffee no matter the time of day or night. The more I thought about it, the more logical it seemed that he would make the coffee at home and bring it to her. Then that idea became head cannon for me From there, a story about how she discovers that he does this seemed inevitable.

I hope you all enjoyed reading this as much as I enjoyed writing it. Reviews are welcome and appreciated.