(Flynn-Fletcher House)
Phineas and Ferb looked around for their sister Candace, who was seemingly nowhere to be found. They looked in the kitchen, in the living room, but Candace was nowhere to be seen. "Huh, it's weird that Candace's nowhere to be seen today." remarked Phineas as Ferb checked the backyard. "Ferb, do you think she went to Stacy's house without telling us first?"
"I think you should take a look at this, brother." answered Ferb.
Phineas immediately went to his stepbrother and the two went to the backyard, only to find a giant, sphere-like dimension with endless roads, not to mention a minute-long timer, instead of the backyard they were familiar with. "Well, I don't remember this being here last time we went to the backyard." said Phineas, right before shouting, "Hey Candace, are you here!"
Phineas received no immediate response, although it didn't matter since his attention was soon taken by a peculiar sight in the skies: a Stacy lookalike with owl wings and similarly owl-like eyes, which was scouting the area. "Hey, maybe that Stacy lookalike can tell us where is Candace!" before Ferb could complain, Phineas loudly called "Hey, do you know where Candace is!"
This got the attention of the Stacy lookalike, who turned and saw Phineas waving hello. This made her turn her eyes red as she released an ear piercing shriek before flying away. "Well, that didn't work." remarked Phineas, sorely disappointed. "I wonder what-"
Suddenly, some vines trapped the boys right where they stood. As they struggled to get out, a bunch of dirt came up and morphed into a humanoid shape similar to Jenny, right before it raised its "arms" and made the vines tighter. "Looks like we won't be leaving anytime soon, Ferb!"
(Meanwhile, back at the house)
Perry slept peacefully on Phineas' bed when he got a call from OWCA. He immediately woke up, took a quick look around and put on his hat before answering the call. He turned to his watch and saw Monogram next to a diagram.
"Agent P, do you have a minute?" Monogram asked. "We've got some strange reading on your owner's backyard. It may have nothing to do with Doofenshmirtz, but this can't mean good news either. Go take care of it."
Perry got up, did the "yes sir!" gesture and immediately headed for the backyard, entering the barrier...and landing in a completely different place from Phineas and Ferb. However, this did allow him to find another sight: a canine Candace, with dog ears and paws for both hands and feet, being brushed by a Jeremy lookalike made of rubber.
Just as Perry realized he was too close to a potential threat, Candace noticed him and started to growl as her eyes became dog-like, only for the rubber Jeremy to calm her down by brushing her hair once more. Seeing that he was fine for now, Perry was caught off-guard when the owl Stacy came in and alerted Candace, who got off the rubber Jeremy and ran after the winged humanoid. Perry promptly adjusted his hat as he gave chase.
(Back with Phineas and Ferb)
The dog-like Candace reached the duo and slowly approached them as they noticed her. "Hey, doggy girl, calm down! We're happy to see another person here but-" once the dog girl got close enough, however, made Phineas realize something. "I think...are you supposed to be Candace?"
The canine teenage girl started sniffing her brother and stepbrother, tickling Phineas and causing him to laugh out loud. The witch recognized the laughter and licked the boy's cheeks before the timer on the world reached 0, and a giant, eye-less replica of Linda Flynn came out of the ground, which instantly caught the witch's attention and caused her to run after her.
Soon after she left, the owl Stacy lookalike and restraining Jenny lookalike vanished from existence, freeing the duo and allowing them to...chase after Candace as well? "Come on, Ferb! We gotta find out why Candace turned into that form!" exclaimed Phineas.
And as they ran, a familiar figure stood on top of a tree, her cape blowing in the wind as she took a huge leap ahead of the boys.
Back with Candace, the watchdog was stopped right on her tracks by Perry, who stood his ground and defiantly gesturing the canine witch to fight him. So the witch, believing the platypus was stopping her to get to the eyeless version of Linda, stood her ground and got ready to attack, baring her teeth in an attempt to intimidate the monotreme.
The duo rushed towards each other...and Perry found that Candace was a tad bit stronger and faster than usual. While he managed to get a couple hits in, Candance mercilessly scratched and attacked the platypus so fast, it almost looked like she was doing multiple things at the same time. The monotreme dropped to the ground and his hat fell off as the canine girl lurked for one final strike.
She got ready, lunged towards the animal...and was then struck by a kiss mark. Which blinked a couple times before blowing up and killing the witch just as Phineas and Ferb arrived. As the smoke cloud from the explosion started to dissipate, the barrier turned back into the backyard of the house, and Candace's grief seed fell and landed on the ground below the smoke cloud.
The duo went to get the seed while Perry grabbed his hat and left before he was spotted. "No need to thank me." said a familiar voice.
"That voice..." said Phineas.
Suddenly, Isabella Garcia-Shapiro jumped down and revealed she was wearing an outfit similar to her usual dress, only with a longer skirt, a pair of fake wings on her shoes and heart-shaped headband, and a cape with a pink heart printed on it.
"Isabella!" exclaimed Phineas as the girl turned around and gave the duo a smile, revealing she had a heart on her forehead. In addition to that, she had a sash filled with patches except for a single space where her soul gem was stitched in. "Where did you get that outfit?"
"It's a long story, but for now, let's just say that I think the deal was worth it." answered the girl before scanning the duo. "Are you okay?"
Phineas nodded and the trio went back inside as Perry adjusted his hat...and then spotted Kyubey nearby. The monotreme got on a fighting stance, only to be surprised when the incubator failed to act like he wanted to fight back.
"I'm done with your universe...for now at least." stated Kyubey. "You can trust me: I will return when the quota updates and reveals whether that witch wasn't enough."
With that said, Kyubey jumped away and Perry narrowed his eyes as he watched the creature leave. Afterwards, he walked back to the house, glancing back at the fleeing creature before he took off his hat, entered pet mode and went inside.