Disclaimer: I do not own Phineas and Ferb or Dexter's Laboratory, or The Adventures of Jimmy Neutron but the last one has nothing to do with this story. This story was written purely for my enjoyment and was posted on fanfiction for the enjoyment of others. I'm not making a cent for this, my only reward is getting this idea out of my head.

A/N: This story was partly inspired by my ex. I have no problem with Lawrence I think he's a great dad but I have to wonder about Phineas' biological father (and Ferb's mother but I have no ideas for her).

Linda Flynn-Fletcher is getting ready to leave she had her purse her car keys she was just about to go when the door bell rang. She opened the door to a tall, skinny man, with curly red hair; he was wearing thick glasses, purple gloves, a white lab coat, and a green backpack.

"Dexter, it's been awhile." She said giving him a hug. "I haven't seen you in over a year."

"Wow that's a sentence that came up way too often in our marriage."

"That's true, hey how is that new think tank going."

"Well, but I can't say anymore."

"Of course you and your secrets so they gave you the day off."

"The week actually I requested a few days off last year and it finally got them."

"Well I have to go shopping, Lawrence is at work. Candace is in her room. Phineas is playing in the backyard with Ferb and Perry."

"I still think its odd having a pet platypus."

"You had a pet monkey."

"Good point"

"You don't mind being alone with the kids do you?"

"Of course not, they're my children I'll be fine watching them…and Ferb."

"They're usually fine on their own so you'll just be spending time with them. Are you staying for dinner?"

"Oh no, I don't want to be any trouble."

"Nonsense it's no trouble, I'll just pick up a little extra."

"Well if you incest, I would really like that."

"So what do you guys want to do today?" Phineas asked his friends, including Irving.

"Perhaps we can build a rocket ship and-" Baljett began.

"No Phineas and Ferb already did that." Irving interrupted.

"It's such a nice day how about we just play tag?" Isabella suggested.

"Running around in circles chasing each other? And then just tagging not hitting, lame." Buford declared.

"Just running around? Ferb I know what we're gonna do today." Phineas announced (as the background tune played).

"Hey kids I'm going to the store I'm going to the store. But look who's here to watch you." Linda stepped back to let Dexter step into view.

"Who's that?" Isabella whispered/asked.

"That's Phineas' dad." Irving answered.

"Oh, hi dad," Phineas said waving to his biological father. "We're going to play tag you wanna join in?" he offered.

"Maybe later, I have to say hi to your sister first."

"You really should play with them," Linda whispered to him. "Bye kids. Hey where's Perry." They shrugged, "you kids should really watch him closer." Linda walked to her car just in time for Candace to appear.

"I'm in charge; you told them I was in charge right?"

"No because Dexter's in charge."

"Dad's here?" Candace ran off to the back yard. Spotting her biological father she quickly wrapped him in a hug.

"Hi sweetheart," Dexter said hugging his daughter.

"Oh is Aunt Dee Dee here too."

"No she's in Porkbelly with your Uncle Johnny. Now I'm going to play tag with Phineas and his friends if you want to join in."

"Actually we can't start for another half an hour." Phineas corrected.

"Oh in that case I want to show you my room." Candace said dragging he father away.

30 minutes later

"Aw you still have the Ducky Momo I gave you when your mother and I got divorced."

"Oh yeah I forgot you gave me that. I guess that's why I latched onto him so much." A scream of excitement was heard as Phineas flew by Candace's window on his jetpack. "Oh, my, gosh dad come look at this." They poked their heads out the window to see Phineas, Ferb, and everyone else flying around on jet packs.

"I can't believe it." Dexter grabbed his backpack as he and Candace began heading for the backyard.

"Neither can I, I've been trying to show this to mom all summer."

"This has been going on all summer and they've been hiding it from Linda and Lawrence?"

"Yes, Yes." They walked outside. "Phineas," Candace shouted causing everyone to look at her. "You are so busted."

"I can't believe this son; I can't believe that…you started without me." Candace turned to him in shock. Dexter smiled as his backpack was torn apart by his robot exoskeleton (which looked exactly like his old Dodge ball suit). He flew up between them, "So who's IT?"

"You!" Phineas shouted before flying away.

"Bad move kiddo." Dexter said before he shot off after him.

Twenty minutes (and one song about jetpack tag,) later everyone had put away their jetpacks and sat and watched as Dexter horsed around with Phineas and Ferb in their Beak costume. Dexter had The Beak in a headlock.

"Give up Phineas I am your father."

"I know but you're still going down old man." The Beak slipped out and picked Dexter up when Linda walked into the yard, with groceries in one arm and Perry in the other.

"What is going on here?" She shouted angrily. "Dexter what are you doing?"

"Mom it's not just him the boys have been doing stuff like this all summer." Candace informed her. Dexter pushed a button and his Exosuit folded itself back up and then produced another backpack around itself.

"Linda I can explain."

"Really," She asked raising an eyebrow.

"No," Dexter pulled out a device that looked like a TV remote and fired a beam that caused Linda to rewind. "Quick hide your suit."He instructed Phineas the Beak flew into the tree, Phineas and Ferb rushed out as Linda once again walked into the backyard.

"Hey kids look who I found in the driveway."

"Oh there you are Perry," Phineas said with a smile.

"Did you guys have fun?"

"We sure did this Dad's really cool too." Phineas said happily

"As the saying goes the apple doesn't fall far from the tree." Ferb stated.

"I thought you were mute." Dexter said slightly confused.

Linda went inside to prepare dinner and all of Phineas and Ferb's friends left. Dexter walked over to Candace who was sitting on the ground moping.

"What's wrong sweetie?" Dexter asked sitting next to her.

"I finally busted my brothers and you don't care. On top of that you like them better than me now."

"That's ridiculous; Phineas and I just finally have something in common. He always reminded me of my sister with his carefree attitude, but now I know he's an inventor like me." He put his arm around his daughter, "you know when I was there age I had a secret Laboratory and only my sister knew about it. I would spend my days inventing, and shouting at my sister to leave me alone."

"Really," she said with a slight smile.

"Oh yes everyday she would come in and annoy me, at times I considered telling my parents about my Lab just to tell on Dee Dee for being in it. Today is the first time I saw myself in Phineas, I always thought the two of us were so different and we are, while you and I were so similar. Phineas may have my brains but you've always had my personality, your musical talent that came from your mother."

"You know dad it was really nice seeing you today."

"Thanks Sweetie and I want you to know you'll always be my little girl even if I don't get to see you and Phineas nearly as often as I'd like to, and I can only call you on your birthday."

A/N: This is a one-shot so that's it.

I just want to say in this reality Dexter and Linda got divorced when they were drifting apart and before they started to hate each other. Also after their divorce Linda reunited with her childhood sweetheart Lawrence. She had met him while he was on vacation, and he and his son just moved to the tri-state area. I say this because of they went to that Love Handle concert in that flashback, pretty sure he said it was his first kiss too.