(Scene opens up in the Flynn-Fletcher house kitchen)
Stacy(from inside) Futons, bouillon, platypus food... (Cut to her, looking in a pantry.) Ooh! Microwave popcorn! Need this.
Candace: And I have sodas. What else do we wanna bring over your house?
Stacy: Doesn't matter. I doubt we'll not be able to eat while we're watching this movie.
Candace: The Grievance. So scary no one over the age 45 will even watch it!
Stacy: It will be even scarier 'cause my family's out for the day and we will be alone at the house.
Candace: Great!
Stacy: Candace, are you sure you can handle this? (They go out to the backyard.) It took me four days to pry you out from under the bed last time we saw a scary movie. (outside) What? What are you looking at? Oh no.
Candace: Phineas and Ferb! What are you guys up to?
Phineas: It's a surprise for Isabella's birthday!
Candace: A surprise...
Stacy: Here we go again.
Candace: ...for Isabella's...
Stacy: Give me those sodas. (She grabs the sodas Candace was holding)
Candace: ...Birthday.
Stacy: See ya. (She walks off)
Phineas: Building supplies? Check. Guest list? Check. Perry? Hey, where's Perry?
Stacy: (Still leaving) Yeah, where does that platypus go everyday?

(In Perry's lair everything is dark except for the Major Monogram on the screen.)
Major Monogram: Agent P.? (The lights flicker on) Ah, there you are. What do you think of the new motion sensor lights we've installed in your lair. (The lights go off again) Um... Agent P. try flailing your arms about that should- (Agent P. does so and the lights turn on) There we go! Now, Doofenshmirtz has been driving around town in some sort of truck that turns inanimate objects, like parking meters, into bugs. Eww. I want you to-- (The lights go off in where Major Monogram is) Really? Carl, I'm waiving my arms, why aren't the lights coming back on?
(Carl laughs evilly)
Major Monogram: That's not funny, Carl.

(In the backyard Ferb, Candace, Buford, Adyson, Gretchen, Katie, Milly, and Holly listen to Phineas.)
Phineas: Okay, time to commence operation INAP.
Adyson: (To Candace) That stands for Isabella's Natal Anniversary Party.
Candace: I know what INAP means. Just get to the dangerous part I'm readying the phone.
Phineas: Okay everyone, we need to carry all this stuff over to Isabella's backyard, so we can set it up for--
Isabella: Hi, Phineas. What'cha doooin'? You're not planning something for my birthday, are you?
Phineas: Don't look, don't look, don't look! Nothing to see here.
Isabella: Phineas! But all I really want for my birthday is-
Phineas: Don't ruin the surprise! (He laughs nervously) Buford, get her out of here.
Buford: You got it. (He throws a bag over Isabella and carries her out)
Isabella: But what I real-
Buford: I've carried a lot of squirmin' bags in my time, but this is the first time I knew who was in it. (He walks off)
Isabella: Augh! What I was going to say was all I want for my birthday is some alone time with-- (motions to Phineas) Never mind. (She walks out)
Baljeet: You wanted to be alone with this bag?

(Song: "Isabella's Birthday Song")
Isabella: Today is my birthday and there's just one thing I'm wishing for
To spend some time alone with a certain someone I adore
It doesn't have to be formal or fancy
It's not a deal breaker if it's not romancy
After all of this time, I've lowered my expectations
Baljeet and Buford: Expectations...
Isabella: Don't need a limo or a corsage,
Just him and me without the entourage
And I won't be upset (I won't be upset)
At this emotional roulette (Emotional roulette)
I'll take any little thing that I can get...

Like eating some french fries: I'll take it!
Stuck on a tarmac: I'm good! (I'm good!)
Trapped under rubble: That's awesome! (That's awesome!)
Moving a piano: If we only could!

Getting orthodontia: Sign me up! (Sign me up!)
In a smelly subway car: I'm in! (I'm in!)
We could be reupholstering a love seat:
I call that a win-win!

'Cause that's all I really want;
Just time alone with my triangular savant
I'm not asking for the world; I'm just a simple girl
And I would change my mournful tone...
If we could just be alone
Just be alone...

(She arrives at her backyard)
Phineas and kids: Happy birthday, Isabella!

(Perry chases after Doofenshmirtz's trucks, and uses a wooden ramp he packed, he launches himself on top of the truck)
Doofenshmirtz: Perry the platypus? It's no use trying to break through my protective bubble. It's platyproof-poof. I mean, oh you know what I mean. Anyway, you're probably wondering what I'm doing, driving this evil bug bus around town. I just got to thinking about all the things that bug me. Portable outhouses, high voltage signs. "Danger High Voltage". I'll decide how much voltage I can take! That's why I created the Bugs-me-inator. It turns whatever bugs me into bugs. And, since I can't stand bugs, I'm protected from them inside this bubble. (Perry points to a bug inside Doofenshmirtz's bubble) Huh? Oh, that's on the outs-- Ow! Get it off! Get it off! Get it off! Get it off! (Doofenshmirtz open the bubble to let the bugs out) Wait I'm not ready! (Perry punches him, causing him to spin around his bubble) Whoa, whoa whoa. Right to the point huh? You know Perry the Platypus, more than anything, you bug me. (He fires the -inator at Perry, who dodges it, making the beam, instead, hit one of Doofenshmirtz's shoes) Ah! My shoe! Ow Get off! Get off! Get off! Ow! (Doofenshmirtz launches himself at Perry, but Perry redirects him back into his bubble, spinning him again.) Whoa. Whoa. Whoa. Boy I really got to rethink the design on this think. By the way, you know we're on a runaway bus careening at high speed with no one at the wheel, right?

Stacy: (To the movie) Don't go in there. Don't go in there. Don't go in there. Don't go in there. You went in there. Oh, gross she brought thousands of tiny bugs into the house. What could be worse than that? (Doofenshmirtz's bus crashes into Stacy's house) Big bug! Ahhh! (Stacy hides behind the couch) OMG! Perry! What are you doing here?! And why are you wearing a hat? Look out! (Doofenshmirtz flies onto the couch) And who's this pharmacist?
Doofenshmirtz: Really? Really? W-why does everyone just stampede to that conclusion? Other people wear lab coats you know. Why, why don't you say, "Oh look a rocket scientist." Or a veterinarian?
Stacy: Are you a veterinarian?
Doofenshmirtz: No... But that's not the point.

Phineas: Check it out. (Isabella's massive cake is seen being wheeled in.) We made your favorite, a red velvet cake, with a little surprise.
Baljeet: Ooh, I hope they do not have a male dancer popping out of it.
Buford: They asked, but they couldn't afford me.
Phineas: Will you do the honors Ferb? (Ferb presses a button, and the candles light.)
Phineas: (To Isabella) Make a wish.
Isabella: (In her thoughts) I wish for time alone with Phineas.
(She blows out the candles, and streamers and confetti pop out)
Holly: (To Candace) What are you doing?
Candace: Waiting for things to get dangerous, so I can my mom to come bust the boys.
Holly: That's not dangerous?
Candace: Dude, this is nothing, it'll get worse.
(Back on top of the cake)
Phineas: So, did you get what you wished for?
Isabella: Uh-
Buford: Yeah, it's every girls wish to have her backyard covered in litter. Let's go you two. Next event.
Phineas: You're gonna love this.

Stacy: Is this where you go everyday Perry?
Doofenshmirtz: (While fighting Perry) Oh yeah, pretty much. I create -inators, and he breaks in and thwarts my scheme, and it's, it's kinda our thing. (Perry knocks Doofenshmirtz to the ground) Ooh! The Grievance! I saw this in theaters. I still have nightmares about the greasy little girl who comes out of the base--
Stacy: (Still behind the couch) No! Don't tell me how it ends!

Phineas: And, now, what's a birthday party without a piñata the size of your house? Ferb? Hit it. (Ferb breaks the giant piñata with a giant bat, releasing smaller ones for everyone else to hit.)
Adyson: Woohoo!
Ginger: I'm gonna bat with this stick.
Gretchen: Give up the candy, yo!
Holly: (Still speaking with Candace) This isn't dangerous enough?
Candace: We're getting there.
Baljeet: Isabella, this must be your best birthday ever.
Isabella: (A little sadly) Yeah, sure. It's super cool. I didn't need--
Buford: Okay Birthday girl, onto the next. (He trows a bag over her, and deposits her at her pool)

Phineas: Gather 'round everyone, and keep your eyes on the pool. Isabella, it's grand finale time! (He pulls a lever, and the pool begins to shake.)
Holly: Um? This might be the time to call.
Candace: Yep! (She dials Linda) Mom? You've got to come across the street immediately.
(The structure continues to rise out of the pool.)
Kids: Ooh!
Milly: What a grand, and glorious, and potentially bustable gift!
Adyson: I've never seen anything like it!

Linda: That key? That key?
Candace: Mom! Mom!
Linda: Here, grab these will ya?
(She passes the groceries off to Candace.)
Candace: Mom, you've got to see what the boys are doing in Isabella's yard!
Linda: Isabella's yard? That's a new one.

Stacy: Alright, look. You're getting oil all over the place. Someone's going to have to-- (Stacy trips, and falls in the pool of oil.)
Doofenshmirtz: No! It's the greasy Grievance girl from the basement! No! No! What have I done? Why do you have a grievance against me? (Doofenshmirtz screams, and jumps out the window)
Stacy: (Fixing her hair) Whoa. What was that all about? Do the Flynn Fletchers know you fight evil scientists? (Stacy accidentally steps on the remote firing the -inator, and Perry whacks it with a bat, destroying it. The -inator beam bounces off a satellite and heads back towards Earth)

Candace: Back here, Mom.
(The -inator beam hits Isabella's gift, turning it into butterflies.)
Isabella: Butterflies? I love butterflies! Oh, thank you Phineas!
Phineas: (Confused at how the gift turned to butterflies) What?
Candace: But, but, but, but, but... Butterflies?!
Linda: Oh, how beautiful. How long did it take you guys to collect them all?

(At Stacy's house, Monogram shows up, disguised as a Danville Water and Power employee)
Major Monogram: Let's go boys, looks like we've got some cleaning up to do. Alright you and you begin with the pavement area around here. And you... (Monogram rings the doorbell) Danville Water and Power. We're here to read your gas thingy.
(Perry leads Stacy outside)
Stacy: Perry? What is all this? (Perry hands Stacy a pamphlet) A-a host family, mind erasing, balloon coverup? I mean is all this really necessary? (Perry shrugs) Wait a minute! It says right here in your silly little pamphlet that if your host family finds out about your agent status, then anyone who's seen you has to have their memory erased, or you'll get relocated. Perry, I'm not part of your host family!  I know, I know, it's a technicality. Look, I don't want Candace and the boys to lose you, but I also do not want my mind erased. I'm on the last ten minutes of that Grievance movie, and I don't want to have to watch that whole scary mess again. So, uh, can we just keep this a secret? (Perry smiles and tips his hat to Stacy)
Carl: Luckily Sir, it looks like the residents were not home.
Stacy: (At the front door) Hello? Uh, anybody there?
Major Monogram: (To Carl) I'll take care of it. (To Stacy) Oh, hello there young teenager. You live here?
Stacy: Yes. I walked home from the mall to find... this. What is happening here?
Major Monogram: Oh, you didn't see what happened? Well, um. We're with the city, and there was a swamp gas incident here. We'll just get it all cleaned up, and get out of your hair. (He turns to Carl) Psst. Hey Carl. We're not going to need the mind erasing device. (He looks back at Stacy) I mean monkey wrench. Hehe. Monkey wrench, we don't need that.

Katie: Happy birthday, Isabella!
(The Fireside girls begin to leave)
Isabella: Thanks guys!
Phineas: I still can't figure out what went wrong with the grand finale. After the laser light show, and the fireballs, the swans should have been released, and-
Isabella: Phineas, I really liked the butterflies. Thank you.
Phineas: Well to make it up to you, it's kinda lame but... maybe Ferb and I could, I don't know, take you out for some ice cream or something?
Isabella: Uh-
Ferb: I...just remembered there's...something I need to do. You two go.
Phineas: Is that cool?
Isabella: Yes! Very cool. Ferb.
(Isabella fist bumps Ferb.)

(At the Soda Fountain)
Phineas: So, did you get what you wished for? Oh, yeah, I already asked that. Confetti, and streamers. Hold on, gonna get another napkin. (He goes off)
Isabella: (romantically) And butterflies, you always give me butterflies.

End Credits

Da da da da
Candace: (From her window) Ah, look at them out there. What are they up to? Ah, it looks like Phineas is saying "Where's Perry?" Huh. Where do you think Perry goes everyday Stace?
Stacy: (Quickly and nervously) How should I know!? Why are you asking me!? How should I know!? Don't look at me!
Candace: (She stares at Stacy for a moment) Nah, I don't know why I was asking you.
Stacy: (In her head) Whew, no one suspects a thing.