So, this idea popped in my head the other night, and I had to write it!

Spoilers: Some for last Monday's Castle episode "Blue Butterfly".

Disclaimer: I don't own Castle or Dr. Horrible's Sing- A- long Blog. They belong to Andrew Marlowe and Joss Whedon respectively. Also, a little boy singing the song I used is on Youtube. It's so adorable!

Kate Beckett was sifting through clothes that were on a rack at a clothing store. She had been there for about an hour and a half shopping for clothes to take on vacation when out of the corner of her eye she saw a girl about eight years old playing in the clothes rack.

"Vera Nicole." She said immediately stopping the child's actions. "You know you're too old to play in the clothes racks." She told her.

"But I'm bored Mom!" The girl said her blue eyes pleading to leave. Knowing her daughter was tired, she took a deep breath. She did not need to buy anything on that rack anyway.

"Okay, go get your brother and we can go." Kate said.

"Do you think we can get ice cream after this too?" The child questioned. Kate rolled her eyes, smirking at how much the child acted like her father.

"We'll see Nikki." Kate answered, "Go get your brother." Nikki happily ran off to retrieve him. A few minutes later, the girl came back alone.

"Where's your brother?" The detective questioned. The child shrugged.

"I couldn't find him." She answered.

"Are you sure?" Kate asked fear starting to rise in her. Nikki nodded.

"Where was he when you last saw him?" The detective questioned, not wanting to cause herself some sort of heart attack or show her daughter how scared she was.

"We were playing in the clothes racks and then you caught me." Nikki told her. Kate sighed.

"Okay, show me where." She said. Nikki led her mother to where she and her brother were playing.

"J.D." Kate asked pushing the clothes back. The child was not there. The woman turned to her daughter, "Are you sure it was there?"

"Yes." Nikki answered. Kate ran a hand through her hair.

"Alright." Kate responded standing with her hands on her hips thinking of any possible place her son could be hiding. Quickly, Kate grabbed her daughter's hand and took her to the front desk. The woman looked at her and smiled.

"Do you need to check out?" She asked.

"Not at the moment. I was wondering if you saw a four year old boy with brown hair and hazel eyes around? He has a black shirt on with a hammer on it." Kate asked giving a description of her son.

"No, I don't think I have. Do you want me to announce it?" The woman asked.

"Yes, please!" Kate told her. The woman picked up her phone and placed the announcement over the intercom. After a few minutes, Kate was beginning to panic, tragic scenes running through her head. Give it to a homicide detective to think of worse case scenarios. A few minutes after that, Kate thanked the woman before going to find her son again. She and her daughter went back to where they were earlier to search again.

"It's like being at work with you." Nikki commented. Kate didn't respond. If the problem at hand were not as dire, she would probably laugh at the comment, but not now. She needed to find her son.

"J.D.!" Kate called again this time with the help of her daughter. The woman stopped at the edge of the clothing section when she saw a small crowd growing around a display model. Kate's eyes went wide as Nikki started to giggle. In front of them was Kate's son singing and acting out, "A Man's Gotta Do" from Dr. Horrible's Sing- A- Long Blog.

The boy was at the part where Captain Hammer was singing to Penny, and not being able to resist, Kate caught the action on her camera. Before he could get any further, Kate made her presence known, knowing her glare worked just as well on her son as it did his father. Gulping, the boy stopped.

"Joe Derek Castle." Kate said. The child looked at his sister for help. Nikki just shook her head not helping her brother out of this one. The woman grabbed her son and gave him a hug.

"Don't ever do that to Mommy again! Do you hear me?" Kate said drawing away from the child as she said the last part. J.D. nodded knowing he had done something wrong.

"I not sing anymore?" He asked. Kate grinned and shook her head.

"How about the next time, you just sing in front of Mommy, Daddy, Nikki, and Alexis." She told him. The boy nodded. After paying for their items, the mother happily left the store with her children.

Entering the apartment a little bit later, the kids ran to Castle and hugged him.

"Hey guys!" He said giving his children hugs and kisses. Kate stood to the side waiting to kiss her husband.

"You look exhausted. The kids wear you out?" He asked drawing back from the kiss.

"Just your son." She stated.

"He's not your son anymore?" Castle questioned, his voice teasing.

"Not when he runs off to start his one person show." Kate told him. Castle stared at her. Kate decided to elaborate.

"We were getting ready to leave and Nikki couldn't find J.D. Needless to say, we looked everywhere for him, even called the desk. When we went back to searching, we saw your son singing a certain song from Dr. Horrible's Sing- A- Long Blog." She told him. Castle grinned a sheepish grin. J.D., seeing the grin on his father's face said, "I sang like Grandma!" Kate and Rick rolled their eyes.

"Guess you'll have to show her bud!" Castle told him.

"Now?" The boy exclaimed. Castle shook his head. "She's coming over for dinner, we can show her later. Go play. Dinner'll be ready later." He said. J.D. and Nikki nodded before running off to their rooms. After the kids left, Kate smirked.

"What?" Rick asked.

"I have it on video." Kate told him. Castle grinned.

"Blackmail?" He questioned.

"Definitely." She smirked.

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