Castle and Beckett argue over who liked whom first.

"Castle, there's no way you're winning this argument."

"Yeah huh," he whined. "It was totally me first," Castle insisted.

They had been taking a trip down memory lane recounting fond memories from early on in their relationship when they came upon a quandry. Apparently they had differing recollections of who had feelings for the other first, hence this animated discussion in bed.

"Nope, I liked you first," Beckett declared decisively.

"No way! I liked you from the beginning, from our very first case! Why do you think I started following you around after that?"

"I know that silly," Beckett swatted playfully at his chest. "And so did everyone else we worked with, apparently."

"Exactly! What could possibly beat that?" Castle asserted self-assuredly. "And a celebrity crush doesn't count. It has to be after we actually met," he qualified.

"Okay fine. I'm still sure it was me though. And I can prove it."

Kate got up and disappeared into his office. She wandered over to the bookshelf to pick out a hardback from one of the rows that contained Castle's novels. Her finger scanned across the spines that each bore his name until it alighted upon the one she was looking for at the far left.

Pulling it from the shelf, she opened the front cover, smiled at a private memory, and retreated back to bed to hand it over to Castle.

"In Hail of Bullets?" he asked. It was his first novel that ever got accepted by a major publishing house.

"Yep. This is my personal copy. Look inside the front cover."

Castle cracked open the hard cover and found an inscription inside of his own handwriting.

Kate,

I hope my words bring you as much joy as your smile brings to the world.

Richard Castle

"When did I sign this?" Castle asked.

"It was during one of your early book tours for Derrick Storm," Kate explained. "I had read the Derrick Storm novels and loved your work so much that I went back and read all your earlier ones. I waited in line for hours to get you to sign it. You probably thought I was weird for not getting a Storm book signed at the event," Kate chuckled.

"Not weird. Flattered. Genuinely flattered," Castle remarked with awe.

"So yeah, now you know how much of a fan I am," she admitted sheepishly. "It's so embarrassing."

"Why? I'm your number one fan."

Kate mentally ran through a reel of memories, thinking over the years of Castle following her around, observing her, writing books about her.

"You are, aren't you?" she said rhetorically, laughing.

"So we actually met before our first case?" Castle deduced.

"Yep. Which means I totally knew who you were and definitely liked you before we started working together."

She could see the gears turning in his head as he processed this new information. Castle opened his mouth to fire a rebuttal, but came up short. He made a few contorted faces until he finally gave up and conceded.

"Fine. I guess you win the 'who liked whom first' thing..." he admitted defeat.

"I knew it," Kate beamed in victory.

"But I loved you first," Castle declared.

That comment gave her pause.

"You did?" Kate asked quietly in a more serious tone. "When did you know?"

"I think it started when I got the offer to write for that British spy series, but that would mean giving up Nikki Heat. I really didn't want to end my partnership with you and that made me realize why," Castle explained. "But I definitely knew after you saved me from Coonan. He was the one lead in your mother's case and you gave that up to save me without a second thought."

"That was pretty early," Kate remembered.

"Mhmm," Castle nodded. "When did you know?" he asked in return.

"That I loved you?" Kate thought to herself for a moment. "I think it was that summer we spent apart after I got shot. I know I pushed you away because I was broken, both physically and emotionally, but not having you with me made me realize how important you were to me. I almost died and almost missed my chance. I didn't want to be apart from you anymore, but I also wanted to be whole for you."

"Oh Kate," Castle breathed.

"So yeah," Kate sighed after that heartfelt revelation. "You won that one," she conceded. "But I think I won because I got you," she affirmed on a high note, leaning in to claim him. He was the best prize she could ever ask for.

"I think we both won that one," Castle chuckled as he brought her in for a kiss. She hummed in agreement.

"Love you," Kate breathed.

He would never, ever get tired of hearing her say that.

"Loved you first."