I'm thinking about his jumping the shark comment and I'm wondering whether the subtext here is that the fans who want to see a Caskett hook-up RIGHT NOW are jumping the shark because it's way too early in the storyline for that to happen.  It's not jumping the shark to assume that they will eventually get together, that's pretty much a given.  What else could he be referring to?

Nathan's repeated mentioning of how Moonlighting jumped the shark is due to the fact that he's simply never been on a TV show that lasted beyond it's second season and he's perhaps overly cautious about getting the fans' hopes up.

Beckett walked into the 12th precinct break room and exhaled heavily as she began preparing herself a cup of espresso.  What the heck am I going to do?  And how did I get into this situation she thought.

Demming.
Castle.
Demming.
Castle.

God, I wish someone published an instruction manual for relationships.  I don’t have a clue what to do about either.  Demming is great, but Castle – Castle is so different.  But can I trust him?  And what about his ex-wife?  She had to come out of the wood work now, didn’t she? 

Beckett took a long drink of espresso and felt the warm liquid flow down her throat, into her stomach and throughout her body.  She hoped it would relax her somehow, or bring her the extra clarity she needed to figure her way out of the romantic pickle she found herself in.  It wasn’t working.  Dammit, she thought and headed back to her desk. 

She stopped dead in her tracks when she saw Castle shake hands with Ryan and Esposito, who took off on an investigation.  Castle then sat down heavily in his usual chair next to her desk.  He looked unusually serious.  This can’t be good.  Her heart fought off the thoughts passing through her brain as she saw him sitting there.  Might as well get whatever this is over with, Beckett thought and continued to her desk.  She sat down.

“Hey,” she began trying to sound casual.
“Hey,” Castle answered.  His voice definitely sounded sad.
“What are you doing here?  The case is closed, so you can go home if you want.”
He inhaled slowly before speaking.  “I know.  I had to see you.”
For a second Beckett’s heart skipped a beat with hope. 
“I had to tell you goodbye.”  Castle’s swallowed hard after saying the words.  He didn’t think they’d be that hard to say.
Just as fast as Beckett’s heart had skipped a beat, it sank into the floor.
“Goodbye?  What do you mean ‘goodbye’?”
“Just for the summer.  My publisher Gina and my agent Paula think that I need to get away for a while.  Change of scenery.  So they’ve put together a book tour, with some stops to promote the Heat Wave movie thrown in too.  I leave tomorrow.” 
Beckett searched Castle’s eyes and face for any hint of a joke and didn’t find any.  “But, what about Alexis?”
“Mother will take care of her for a few days while I’m gone, then this weekend she leaves for a summer program at Oxford that she got accepted into.  She’ll be fine.”
“What about – us?” Beckett asked searching again and trying desperately to hide the panicked feeling building inside her.
“I didn’t realize there was an ‘us.’  I thought there was just a ‘you and Demming.’”
“I mean your shadowing me.  Will you still need to once you come back or do you have enough research for your remaining Nikki Heat books?”  This was the question her mind wanted answered.  Her heart wanted another one answered.

Castle thought for a long minute, one of the longest Beckett remembered experiencing in a long time.  He looked back at her face, that beautiful face, and saw her eyes pleading with him.  Those gorgeous brown eyes that he had dreamed of getting lost in so many times.  He wanted to stroke her cheek, hold her hand, pull her close to him, but he knew it was impossible.  She’s with someone who makes her happy.  She’s out of bounds now.  Taking some time away from her is the right thing to do. 

“I don’t know,” he finally said.  “I really don’t know.”

Beckett sat back in her chair seemingly defeated.  Castle saw the same look cross her face that came out when he cold read her on the first case they worked on together – the look of a heartbroken little girl in search of shelter from life’s cold realities.  For her part, Beckett was in semi-shock.  She realized that she had taken Castle’s presence at the precinct and his help on her cases for granted.  How could she have expected him to always be there?  He’s rich, world-famous and an eligible bachelor.  It was only a matter of time until something – or someone – came along that would put an end to his shadowing her.  She did her best to fight off the tears welling in her eyes, but sensed that he noticed.

Castle tore his eyes away from hers and stood up slowly.  “I’m sorry, but I have to go.  I haven’t even started packing yet.”

Beckett nodded, stood up and took a step closer to him.  Castle extended his hand.

“Take care of yourself, Kate.  Please.”  It wasn’t just an innocent “so long” or “see ya later.”  It was a plea.
Beckett took his hand and shook it.  “You too, Castle.  I hope…”
Beckett looked at the floor boards under her feet and collected herself.  You’re in the precinct!  Pull it together!
“I hope the trip goes well,” she finished.
“Thanks,” he said and began walking towards to the elevator. Beckett followed behind him silently playing with her fingers. He pushed the down button and in a second the door pinged open.

They looked each other in the face what they thought would be one last time.  Castle opened his mouth as if to say something, then stopped himself.  They could feel the rock-hard tension between them and secretly longed for the courage to break through it.  It was Castle who finally made a move.  He stepped forward and slowly leaned towards Beckett, leaving a slow, tender kiss on her left cheek.  He lingered close to her for longer than he should have, breathing in her scent, as if it was the only thing from which he could derive the energy to take with him on his trip.  As he lingered there, Beckett kept her eyes closed tight, trying to permanently etch the smell of his cologne and the feeling of his nearness in her mind.

He finally stepped away and onto the elevator.  He pushed the down button.  They looked at each other as the doors began to close.  The last thing Beckett saw was Castle lift his hand in a weak wave.

Castle walks onto the elevator, pushes the down button and settles himself against the back wall.  As the doors begin closing, he raises a hand in a weak wave, then hangs his head. 

Then suddenly a ping rings out, and the doors bounce back open.  Someone had stuck their arm in the door to prevent it from closing then tumbled inside next to him.  A burst of electricity flowed through him when he saw that it was Beckett. 

“Don’t go, Rick.  Don’t go on that trip with that woman.  Stay here.  With me,” she pleaded.  He had Beckett vulnerable before, but never this much so.  He couldn’t believe how beautiful she still was. 
“I signed a contract.  I have to go.”
“I don’t want to lose you,” she said earnestly, her voice cracking.
He stepped forward, taking her face in his hands.  His chest was heaving.  Her heart was pounding. 
“You won’t.  I promise.”
A smile slowly formed and lit up Beckett’s entire face.  She took hold of the lapels on his blazer and leaned in close to him.  “Good.  Then take this with you to remember me by.”

She wrapped her arms around his neck and kissed him with a blazing passion.  He locked his arms around her waist and held her and kissed her as he had never held or kissed another woman before.  It was as if their lives and the lives of all around them depended upon their being with each other in that very moment.  Finally they pulled apart, but kept their arms in place.
“Castle?” Beckett said quietly.
“What?”
“Did you notice that the doors to the elevator never closed?” A terrified look crossed his face.  Shoot, the button!  She’s totally gonna shoot me!  Ryan and Esposito will shoot me!  No, wait.  They’re gone.  But the others? 

Castle & Beckett slowly turned their heads and saw that a crowd, including, to their shock, Esposito, Ryan, and Captain Montgomery, were watching them as if they were fish in a tank at an aquarium.  Esposito looked pleased, Ryan amused, and Montgomery plain happy. 

We are never gonna live this down, they both thought and looked at each other again, trying to figure out what to do.  Then Castle grinned and looked back at the crowd.  He removed his right arm from around Beckett’s waist, reached out and touched the down button on the elevator.  The last thing anyone on Beckett’s floor saw as the doors closed were both Castle’s and Beckett’s lips meeting again.