This was a team effort with Shanar. But it's mostly mine. :) And yes, I know that there are other stories about Phineas' father, but this was an original idea before I knew that other people thought of it! I promise!

Enjoy!

Chapter 1: Oh, Yeah. Stepbrothers.

Phineas and Ferb sat in the grass, encircled with blueprints. "This is gonna be awesome!" Phineas patted Ferb on the back. "I'll call Isabella and have her bring the fireside girls. We'll need the help!"

Ferb sat and organized the blueprints according to size while Phineas pulled out his phone. He dialed Isabella's number. It rang for a moment, and then Isabella's voicemail took the liberty of answering. "Hey, this is Isabella. Sorry, I'm probably busy right now, but leave a message and I'll get back to you!"

Phineas groaned softly and tried again, but the answering machine didn't seem to care. "…leave a message!" Isabella's voice sang again. "Beep."

"Hi, Isabella. This is Phineas. Call me back when you get this." Phineas closed the phone. "No answer, Ferb."

Ferb shrugged.

Phineas put his hands in his pockets. "Want to save this for another day?"

Ferb gathered up the blueprints and folded them neatly into tiny squares, and dropped them into a shoebox. He put it under his arm and went inside close behind Phineas.

"What should we do today?" Phineas said as he flopped onto the couch.

Ferb sat beside his brother and noticed a copy of Macbeth sitting on the coffee table. He picked it up and began to read.

Phineas wanted to let Ferb enjoy his story (and it's also very hard to recapture Ferb's attention once he starts reading), so he went to the bookshelf in the corner of the room. He had never really looked through these books. He was always outside. Moby Dick, The Odyssey, Team of Rivals, Great Expectations… These weren't really the kind of books that would hold Phineas' attention for long right now. He ran his fingers across the spines of each row of books trying to find something to read. After a few more moments, one book caught his attention.

The book stuck out of the shelf about a half and inch, and had no title on the side. "Hm." Phineas pulled out the book.

It was more of a plastic binder than a book. He turned over the curious book, and saw a simple title in baby blue, paper letters: Phineas' Baby Book.

Baby book, huh? This could be interesting. Phineas hopped back onto the couch and opened the cover. A copy of his birth certificate sat in a plastic protector. He turned the page. I know all that stuff. He thought sarcastically. The next page surprised him, though.

"Ferb!" Phineas gasped. Ferb slowly looked away from his book and looked at the page Phineas was pointing to. There, in another plastic protector, was a glossy photo of a baby Phineas in a little hospital crib and, next to him, a man neither of the boys had seen before. He had a triangular head and big blue eyes like Phineas, and thick, slightly curled blond hair and a short, blond beard. Underneath the picture, written in Linda's handwriting, was a small caption written in blue pen: "Wilson and Phineas, Day 1".

"Who's that guy?" Phineas said. "He looks sort of like… me! Wait a second!"

Phineas and Ferb ran into the kitchen with the baby book. Linda stood at the counter cutting vegetables. "Mom! Mom!"

"Yes, Honey?" Mom turned away from her work to look at Phineas. The boys looked a bit dismayed. "What's wrong?"

"Mom, who's this?" Phineas said, pointing to the mystery man in the picture.

Linda hesitated. "Uh… Phineas, that's y-" Suddenly the phone began ringing with a high-pitched twittering noise. "Sorry, sweetie. Hang on just a sec." She walked over to the phone and put it to her ear. "Hello? … Yes, this is Linda Flynn. Who is this? … Wilson?"

"Mom?" Phineas slapped his hands on the top of his head. Phineas was having suspicions about who this mysterious person was, but now he was calling his Mom! Although the boys could only hear one side of the conversation, they could tell there was irony in the house. And who was this "Wilson" guy? Why was he suddenly appearing so much?

"What a coincidence! Phineas was just- … Phineas and Candace are doing fine, why do you ask? … Oh, I don't know… The whole weekend? What brought this about?"

"Mom, what's-" Phineas began.

"Hold on just a second, Phineas. Sorry, about that. Well, Candace is at Stacey's for the weekend. I'm sure Phineas… Okay. That will work. I'll drop him off tomorrow morning. … Okay, goodbye."

"Mom?" Phineas dropped his hands back down to his sides.

"Phineas, Wilson is your biological father."

Phineas and Ferb exchanged glances. "Okay." Phineas said. "That was… frank."

Mom knelt down and looked at the boys. She put a hand on one of each of their shoulders. "Phineas, you're going to visit your father this weekend."

"Are we visiting for dinner?" Phineas said.

"No, Phineas. You're spending the next three days at his house. Starting tomorrow morning."

Surprisingly, Ferb was the one to make the next comment. "What?"

Phineas stuttered.

"Why don't you pack your things, Phineas?" Mom said with a faint smile.

"Is Ferb coming?" Phineas put his arm around his brother.

"I'm afraid not."

Ferb put his hand on Phineas' shoulder, and the boys stood in a one-armed embrace. Phineas looked at his shoes. "Oh."

"It will be a good experience for you. You'll get to meet your father, Phineas, and… maybe spending some time away from each other will…"

Phineas and Ferb squeezed closer together.

"…be good… for you?" Mom finished hesitantly.

"It's just… Dad is the only "dad" I've ever really known! You know, Ferb's dad, my dad! I've just never really thought of anyone else being my dad. I know Dad is my… stepdad, but…" Phineas' voice trailed off. "It's like my real dad is my fake dad, and Ferb's dad is my dad, but fake dad is my dad!"

"There was never really a "his dad" and "my dad". It was like, "our dad," Ferb said in a soft voice.

"If you start missing Ferb, or Dad, you can call. Okay, Phineas?"

Phineas nodded along with Ferb. They walked out of the room like they were in a funeral procession, still locked together.

The boys walked up the stairs together into their room. Phineas pulled a gym bag out of the closet. "Packing," He said flatly. Ferb sat down on the floor between their beds. Phineas wordlessly pulled out three pairs of blue shorts and three orange striped t-shirts and stuffed them in the bag.