Hi everyone! Sorry about the long wait but I finally got far enough into this story for me to post the first chapter. This is my first crossover, so it's probably not very well put together but hey, at least I tried. :)

Gravity Falls fans, the Pines family doesn't come in until later, but I promise they're in here.

Pardon Phineas' edginess in this chapter... he's not quite himself today.

It was the usual morning for Isabella: Wake up to the sound of the robins outside the window, bid good morning to Pinky, brush the frizz out of her hair, wash up in the bathroom, and throw on the usual outfit. Today was a Saturday in the month of July, and the weather was in favor for something impossible to happen.

She saw her reflection in the mirror, and gazed at it. It was weird, she thought. What if mirrors themselves were optical illusions and what you always saw yourself looking like was completely off? But then again, cameras and drawings by a certain someone couldn't be wrong. The sixteen year-old took hold of her bottle of black mascara and put a light coat on her eyelashes, examining her iris at the same time. The blue streaks that surrounded her pupil glistened like crystals. No wonder Phineas seemed to always stare into them when they were close. Eyes were interesting things to look at. After closing the bottle, she took up a stick of lip balm and applied it gingerly.

Her mind wondered back to the subject of illusion. Although it might be the most interesting side of it, the looks of something, or what you'd see on the outside, aren't always the most perplexing. Sometimes the inside can be just as tricky and obscure. Isabella wondered that maybe what she always thought herself to be on the inside was just an illusion covering what really was there.

She straightened up in the mirror and messed with the hair in front of her ears a bit. She decided to leave it not tucked behind her ear, as usual, because Phineas took a liking for putting it behind there himself. Maybe she would ask him to braid it for her. She took a long look at her outfit. A pink blouse with a fancy collar covered her upper body, and she wore white shorts that rode high on her waist, making it a possibility to tuck in her shirt without it looking dorky. On her feet she showed off pink flats with lace around the rims. She smiled at her reflection and then dashed out the bedroom door. Her hair flew out behind her as she ran down the hall, descended the stairs, dashed through the kitchen (While grabbing a pre-made cinnamon waffle and giving her mother a wave), and almost attempted to run through the closed front door. She slowed down a tiny bit the open it, and then kicked it closed behind her on the way out.

Isabella couldn't hear any construction going on yet, so she assumed her sixteen and almost seventeen year-old friends were still trying to find something to do today. She made her way across the street and past the garage, and laid her eyes on the all-too-familiar orange swing open gate that would guide her into the backyard. She could already see the two boys with their backs up against the towering oak, which had grown over the height of the house now and provided shade for almost the entire backyard.

She placed a confident hand on the gate and pushed it inward as she walked through. "Hey, Phineas. What'cha dooin?" The ring of her catchphrase resonated through the yard.

The eyes of the boys darted up, but they didn't flinch. Phineas gave her a kind smile while Ferb simply waved once.

"Hi, Isabella! Nothing big yet, but I can feel the gears in my brain turning." The red-head answered her, as always.

"That sounds painful." Ferb furrowed his brow and looked at his stepbrother in disgust.

Isabella sat in the warm grass in front of them and leaned on one hand behind her. The leaves blocked all the direct light except for a few rays, and they fell upon the three teens in random places, casting patterns of leafy shadows on their skin.

"Where are my other two boys?" The girl looked around with an elevated eyebrow.

"Baljeet has another polka recital, and Buford doesn't come unless 'his nerd' is here." Phineas said unpleasantly. "Sometimes I think that they're mentally interrelated, and if you separate them a bomb will go off in some really important major city."

Isabella narrowed her eyes. "And it's weird because they're supposed to be bully and nerd. Enemies, not frenemies."

"We've gone over this how many times now?" Ferb wondered, chuckling amusingly on the side.

"Quite a few, Ferb. Quite a few." Phineas agreed.

"Oh yeah!" Isabella suddenly remembered something. "I just remembered, today's Gretchen's birthday! She said she would be by here around four, so we need to get all of our presents hidden."

"Done and done." Ferb muttered.

"We hid them this morning." Phineas said with a grin. "Along with half the cake."

Isabella eyed him. "Half the cake?"

Phineas chuckled guiltily and looked at Ferb, who cracked a devious smile. "Ferb got hungry after breakfast."

"So you thought the only logical thing was to eat half of the poor birthday girl's cake?" Isabella rolled her eyes.

"Everything else looked so dull compared to it. It was just sitting there all sad in the fridge." The British teen said while he shrugged.

Isabella groaned. "You are a bottomless pit, Ferb! And it doesn't even faze you; you're as ripped as an Olympic swimmer!" She poked his belly, and he flinched.

"He's the man of action, what do you expect?" Phineas joked.

Isabella shook her head in amusement. "I expect nothing but the most incredible." She paused and waited for a moment to get back on the subject of her friend's birthday. "So, how are we gonna do this birthday thing? Do you have a concept down for the yard yet?"

Ferb reached behind him and pulled out a purple binder, flipped through the pages until he found it, and turned it around so she could see.

"We came up with this last night." Phineas explained. "The tree's gonna have streamers coming down off of it like a canopy, and the dance floor will be in there. On the outside of the canopy, we'll have some games set up, including spin the bottle, as she requested. We'll also have helium inflated chairs that'll be attached to the ground to sit in, and an assortment of snacks coming from the Farmer's Market."

Isabella nodded in exultant approval. "Awesome! What about light fixtures? You guys got all that down?"

"Uh-huh. We got spot lights, strobe lights, LED laser pointers, a fancy crystal chandelier to hang on the tree, an assorted array of globular bulb lights to hang among the streamers and across the yard, and some candles for when everything starts to slow down." He gasped. "Oh! And we also have lots of lanterns to hang. They're the kind that you can set into the wind at the end of the night. The squares of the dance floor light up in different colors too."

Isabella seemed pleased. "You guys thought of everything!"

Phineas nudged Ferb. "Oh, that's not even half of it. Ferb took it to himself to make an electronic beat synthesizer. Anyone can create their own music to dance to. The preset sounds are mainly dubstep, and the cool bloopy noises. So we can go and sing on the stage to our own music!"

"You guys are making a stage too?"

"Ferb's rebuilding the same one we used for Love Handel like six years ago."

Isabella looked at Ferb and her eyes grew wide. "You're going all out for this aren't you?"

Ferb shrugged. "She's a nice girl. She deserves a nice party."

"I can't wait until she sees it!"

"You said she was coming around four?" Phineas questioned.

Isabella nodded. "Her mom wanted to take her shopping, so they won't be home until then."

"That's convenient, then. It'll take about an hour or two to get everything set up, and Perry has an appointment at the vet at one." Phineas said, shuffling through a note pad. He looked at a page he had written on earlier that morning, stating everything that was to be done today. He normally didn't need a list to remember it all, but for some reason he just felt like writing at the time. He had also doodled a tiny Isabella on the bottom right corner, so he kept the pad close and made sure his face didn't turn different colors.

"Oh, is something wrong with him?" The girl wondered.

"Yeah, he hasn't been acting like his normal self lately, but it's only inside the house. In the yard, he's the same, but inside he just acts really edgy and it's like he's scared of everything. It's almost like he thinks somebody's watching him in the creepy stalker kind of way."

Isabella frowned slightly. "Well that's strange. Pinky's never done that before… but I guess it's not very accurate to be comparing a dog to a platypus."

Phineas shrugged. "He's pretty much like a dog, except for the obvious stuff that makes him a monotreme."

The girl nodded and narrowed her eyes in acceptance. "Yeah, you're right. He does always behave like a normal dog. Besides like… playing fetch and chasing his tail." She giggled. She brought her hair over her left shoulder and stroked it softly.

"So when are we going to set up the party?" Isabella wondered, looking around at the vacant yard.

"I thought he was going to try and think up something else first, as a side project." Ferb thought, glancing at Isabella and then back to Phineas.

Phineas smiled. "Well, if Isabella wants to get to work on Gretchen's birthday, then we can do that now."

They all stood up from the grass and brushed the pieces off of their clothes. Ferb went inside to retrieve the bulb lights and streamers, while Phineas brought Isabella into the garage to get the chandelier. They had decided to piece together the tree canopy first, since that was going to be the heart of the whole party. It was probably going to be one of the most difficult things to set up, though, because they had to find the perfect branch to hang the chandelier on and they needed to make the streamers and bulbs look like they were coming off of it.

Isabella followed the red-head out of the yard and into the driveway, where he punched in the code for the garage door opener on a side panel. The door opened slowly and loudly, and when there was enough space to slide under, they both ducked their heads and went inside. Isabella's eyes went wide when she saw the beautiful chandelier in the soft light. None of the crystal pieces were put on it yet because it would be too risky to carry all of that glass all the way into the backyard. The crystals were all set in three different wicker baskets on the floor under the table on which the main frame sat.

Phineas stepped up beside her and smiled, and he reached a hand up and stroked the back of her head with it. "Do you think it's big enough?"

Isabella nodded slowly in astonishment. "Phineas, it's the size of my refrigerator!"

The boy giggled. "Just wait until we get all of the jewels on it."

"Have you already put it together?" She wondered, walking forward to look at the assortment of different sized and shaped beautifully carved diamonds. "These are…. These are real diamonds, Phineas!"

Phineas crouched down next to her and picked up one of the beautiful rocks. "We made them ourselves. All we had to do was put some carbon under the pressure of eight hundred fifty thousand per square inch and heat it to the temperature of the Earth's mantle. Of course, normally it would take about four days to make a diamond at that rate, so we multiplied the amount by four and the temperature by two."

"Why not multiply the temperature by four also?"

"We tried that, but the heat started making the machine go all wonky. I guess it couldn't stand that high of a temperature."

Isabella picked up one of the jewels for herself and examined it closely. "How did you carve them this intricately?" She squinted at it.

"Ferb is magical."

Isabella glanced at him and then simply nodded. "I see."

Phineas then stood up and picked up the frame of the soon-to-be chandelier and Isabella took the smallest basket of diamonds. They were quite heavy.

"You got 'em?" Phineas held a hand under the basket when he saw her struggle a bit.

"Yeah." She looked up and smiled. He smiled back, and then they both took the objects into the yard and set them under the tree. They made one more trip to the garage for the other baskets.

Ferb stood under the tree when the two got back from the second trip. He was untangling the bulb lights and straightening them out on the lawn.

To Isabella, something seemed off about today. Something just wasn't right, and she couldn't put a finger on it. Maybe it was because Baljeet and Buford were gone? She wouldn't get this feeling on any other day that they were missing from the group, so that couldn't be it. The inventor and the craftsman were both at ease, and nothing seemed different about them. Phineas was still oblivious yet showing signs of love, and he still spoke in really big manly words. Ferb was still his mysterious yet charming self, the same boy who always made her laugh and who was her best friend since as long as she could remember. But yet, something wasn't blending into the background of it all. Something wasn't fitting. Something didn't belong. But what?

Ferb took out a small hand-held strange looking canon thing and put one end of the lights into it, and then he proceeded in shooting them up to their place in the tree. The lights cascaded from the branches to the roof and back again around ten times, and it formed a shelter of bulbous bulbs. Isabella concluded it would look magnificent when the dark night rolled in.

Phineas used a system of climbing up into the tree to the designated branch so Isabella could hand him the chandelier to hang. He used a thick rope to tie the frame to the tree, pulling it hard to make sure it wouldn't fall.

"Hey Izzy?" He called, and the girl blinked at him in wonder. "Can you make sure this won't fall for me?"

"Sure, Phineas!" Isabella said happily. She then jumped as high as she could and latched onto the metal on the first try. It didn't budge, but it did swing a little. She began to move her legs back and forth, and it swung with her. Phineas giggled at her monkey-like actions.

"Do a flip." Ferb suggested as he watched her.

The girl grinned and beat her legs back and forth until she gathered enough momentum to perform the proposed trick.

"Izzy, don't do it, Ferb's a dumb butt!" Phineas shouted worriedly from the shaking branch above her. He backed up off of it and got in the center of the tree, then made his way down the trunk.

Isabella took one last thrust forward, and she had the confidence in herself that she would make it. Or perhaps it was the confidence that someone would catch her before she would break her sorry behind. She leapt through the thick air and tucked her appendages into her chest, and she did one full spin in the air before coming to a final (but incomplete) stop in the arms of Phineas. He then stumbled backwards and fell into Ferb, who managed to keep him up on his legs.

When the stop became complete, Isabella looked up at her knight in shining armor, and gave him an innocent smile. He furrowed his brow.

"ARE WE ALL FROM CRAZYTOWN!?" Phineas shouted.

Isabella blinked at Phineas and frowned slightly before pointing at the one with green hair. "He's the one who gave me the idea."