A/N: Beginning of season 7. Prompt posted at the end.
Ryan hung up the phone and did a victory fist pump, then called across the bullpen, "Beckett, we're on. You up?"
"Of course," said Kate, grinning. "You better hope a body doesn't drop in the next ten minutes. Are you dropping off, or am I coming over?"
"If you could come over, that'd be best," said Ryan, coming over to her desk. "We've got leftover pizza if you're hungry."
"Ah yes, my usual fee. That's fine, Kev. Six thirty okay?"
"Perfect. Jenny and I are eternally grateful."
Castle, who had just come back from the break room, sat down in his usual spot and asked, "What was that about?"
"Well, I'm going to be busy this evening, so I hope you weren't expecting me."
"Not expecting. Hoping for, maybe. Anticipating." He narrowed his eyes. "You're busy with Kevin and Jenny? With what?"
"You know my methods, Watson. Guess."
"Menage a trois? In which case I'm crushed that you didn't invite me to even things up. Bowling league? Hard to imagine you in those shoes. Poker night? Again, crushed."
"That's three strikes, Castle. You're out, and I'll see you tomorrow." Kate leaned over, smiling, and kissed Castle's cheek, and he walked her to the elevator, speculating all the way.
A couple of hours later, a text appeared on her phone. It was from Castle.
I'm at the door but I'm afraid to knock. May I come in?
Kate smiled and texted him back.
Door's unlocked. Come on in.
The doorknob turned slowly, revealing her beloved, who sidled in and closed the door just as quietly as he'd opened it. Kate looked up from her seat on the sofa and watched his expression change from apprehension to awe.
"Wow," he whispered. "You're gorgeous. Both of you."
He sat carefully on the sofa beside her, his eyes fixed on the pajama-clad form on her lap, supported by her arms. Sarah Grace Ryan, nine months old and passed out with a well-loved stuffed lamb toy in her grip.
Kate smiled fondly down at the baby.
"She wound down about half an hour ago," she whispered. "I was just about to put her in her bed."
"Let me?" Castle held out his arms.
Kate transferred Sarah Grace gently into his embrace. Then she sat back to enjoy the joy that lit his face as he gazed down at the child, as he must have gazed at Alexis when she was tiny. Kate tried to imagine Castle's daughter that small and failed, but she could picture him as a father perfectly.
"How'd you find out?" she asked softly.
"Ran into the Ryans on my way to dinner," he said. "They were dressed to the nines. Ryan said they were out for dinner and dancing and that you were their Sarah-sitter for the evening."
Kate's smile grew even wider. "So you figured you'd crash the party?"
"Figured you might need backup," he said. "But you're obviously doing fine. This isn't your first gig with Miss Ryan, is it?"
Sarah Grace stirred and Castle shifted her to put her head on his shoulder.
"It isn't," said Kate. "I started over the summer. It's become kind of a thing – they manage to get a night out, they call Lanie, or Kevin's sisters. Or me."
"Guess you're a baby person after all," Castle pointed out.
Kate's smile faded a little.
"I guess she grew on me," she murmured. "We kind of – bonded, over the summer."
"The summer I was gone." Castle's smile faded completely. "Kate, you know I – "
"Hey," she said, leaning over to put her head on his other shoulder. "You don't have to keep apologizing. I love you, and I love Sarah Grace, and it was good to feel like I was doing something good for someone."
"Including yourself," he whispered against her hair.
Much later, the doorknob turned again and Sarah Grace's parents tiptoed in. When she caught sight of the three people asleep on the sofa, Jenny nearly laughed out loud.
"Aww, look at that," she whispered to her husband. "So sweet."
"I don't remember telling her she could have her boyfriend over," said Ryan in mock consternation. He took out his phone and snapped a picture, saving it for the next time he wanted to tease Castle. Or Beckett.
Castle, who sat sprawled on the sofa with Sarah Grace asleep on his chest, and Beckett, snuggled into his arm with her face pressed against his shoulder.
"So sweet," Jenny said again, and they tiptoed upstairs.
A/N: The prompt from castlefanfics was "Season 7, Babysitting Sarah Grace".
