A/N: Howdy! I don't own Phineas and Ferb *sniff*.

WARNING: SPOILERS FOR THE MOVIE!

Okay, I admit. I watched the movie and then Fern (my raptor alter-ego-sort-of-thingie-person-y-thing) said to me, "Ang, I know what we're gonna do today". Cheeky beggar.

Look out for the AVPM reference.

I.O.U One Kiss

Isabella woke up to bright sunlight pouring in through her window. She groaned and tried to pull the covers up over her head, but soon realised it was no good. She was never gonna get back to sleep. Oh well. Her head hurt pretty bad, but maybe Phineas and Ferb could invent something to –

Phineas and Ferb! They must be halfway through inventing something right now! It looked like it was about midday. She should go see what they were doing.

But first she'd better pretty herself up. Today might just be the day that Phineas noticed her.

Isabella nearly shrieked in horror when she saw her reflection. She must have been tossing and turning a lot in her sleep. There were bags under her dark eyes and her long black hair looked awful. And her mouth felt funny. Sorta… tingly. What could that be, she wondered.

Oh well. The hair brushed down; it must've all just gone static, somehow. She couldn't do anything about the bags under her eyes, but a few splashes in the face with cold water woke her up a bit better.

Isabella grabbed her usual pink dress, pumps and bow. Her mother had left some toast on the table for her downstairs; it was cold now, but in her hurry, Isabella didn't notice – she ate it as she crossed the street.

Hmm. It was quiet.

Too quiet.

The boys weren't inventing today.

Oh no. Maybe they were already done! What if they had realised how easy it was to invent without her help? What if they didn't need her anymore? She'd never get to see Phineas again, and then she'd die old and alone and –

"Isabella?"

It was Mrs Flynn-Fletcher; Phineas, Ferb and Candice's mother. Isabella whipped around. "Mrs Flynn-Fletcher! How are you?"

"Oh, I'm good, thanks, hun."

Mrs Flynn-Fletcher had Candice's orange hair and pointy-tipped nose, and the same indigo-blue eyes of both her biological children. Ferb was the stepbrother of Phineas and Ferb, and related to Mrs Flynn-Fletcher by his father's marriage to her. Phineas had very bright, shockingly red hair and Ferb had the opposite: bright, shocking-green. Ferb did not talk much, and his appearance did not always show it, but he was very intelligent, like his stepbrother. Were it not for the obvious differences – Ferb's British accent; Phineas' diamond (or triangle, depending on the angle) shaped head and Ferb's block-shaped nose – it would be easy to believe that they were related.

"Did you want to see the boys?" Mrs Flynn-Fletcher asked. "They just got up – they must be exhausted."

"Sure," Isabella said. Her mind wasn't entirely where she was today. It kept wondering off to a very good – and a very realistic – dream she'd had last night. It was incredibly vivid.

"Um, Major Monogram?"

"Yes?"

"So, none of us will remember anything from today?"

Phineas stared at Isabella. There was an… interesting edge to her voice. It sounded like she was planning something.

"That's right," was the answer.

"Good."

And then Isabella rounded on him. For a minute, Phineas thought he'd done something wrong. Especially when she grabbed his shirt. But then Isabella did something Phineas hadn't been expecting.

She kissed him.

It wasn't a particularly long kiss, and it wasn't particularly passionate. But Phineas could feel years of pent-up emotion coming from Isabella. When she pulled away from him, there was a wide smile plastered on his face, and he had to take a breath to steady himself.

"Isabella!" he was shocked, but in a good way. There were no other words for it. Had he missed something? His mind was still a bit fuzzy round the edges; she'd really caught him off-guard.

Pleased with his reaction, Isabella turned back to the secret agents. "Hit it, Carl!"

Wait a second… Phineas didn't wanna forget this. "Wait!" he cried, trying to stop them from wiping the memories of himself and his friends. "Wait, wait!"

Too late. There was a flash of bright light and –

Phineas sat upright in his bed. He was confused, he was tired, his head throbbed, and the last thing he remembered was –

Woah. Some dream.

Phineas hadn't realised his subconscious was capable of creating something like that. And it had been so vivid, too.

Huh. Weird.

Waking up a bit better now, Phineas saw the bright, midday light filtering in through the windows, and checked his clock. Oh man! Half the day was gone!

"Ferb! Wake up!"

His green-haired stepbrother sat up groggily, rubbing his eyes.

"It's the middle of the day!" Phineas shouted frantically, jumping out of bed and rushing downstairs, still in his pyjamas. Ferb followed.

Candace was up as well, but only just. She looked almost asleep and her hair was a mess.

"Oh, good morning, boys," Mom said. "Well, I suppose it's good afternoon now. Do you want some bre – ah, lunch?"

The boys hadn't realised how hungry they'd been until Mom put a large plate of sandwiches in front of them. They dug into their food and it made their heads feel better.

"Isn't that Isabella outside?" Candace asked suddenly. The sound of Candace's voice made Phineas jump. He'd almost forgotten his sister was in the room.

"Oh, I'll go get her then," Mom said.

Mom went outside to invite Isabella in, and Phineas was suddenly all too aware that he was still in his pyjamas. Wait – why did he even care? Something like this had never bothered him before, so why should it bother him now? Something weird was happening.

"Woah," Isabella said, walking in. "You look awful."

No kidding. Phineas realised his and Ferb's hair was all sticking up on end and they had bags under their eyes, and they were pale. Granted, Isabella looked tired, as well, but still…

"Yeah," Phineas joked, laughing nervously. "I guess we musta had a long day yesterday, huh?"

Isabella paused as she slipped into a seat next to him. "You mean… you don't remember anything about yesterday."

"No. I just remember having a weird-crazy dream, and waking up this morning."

"Me too."

"Huh," Phineas said, distracted. He looked at Ferb and Candice, both of whom shook their heads – they didn't remember yesterday, either. "That's weird. What did you dream about?"

Isabella blushed. Oops. He'd asked the wrong question.

"Oh, er, nothing important. You?"

"Same," Phineas lied. He didn't feel comfortable lying to Isabella, and he could feel the colour rushing into his face. "I, uh – yeah, nothing. Um, I'm going to call Buford and Baljeet over."

Phineas shot into his room and hurried to change into his usual stripey orange-and-white t-shirt, blue shorts and sneakers. He looked better, having eaten something, but he didn't know that.

Having called Buford, the large, pale bully, and Baljeet, a small nerd from India over, Phineas waited nervously in the back yard for them. He paced back and forth, stressing out, until Ferb joined him.

"Hey guys," a deep voice yawned. Buford and Baljeet looked terrible, too.

"What is your big emergency, Phineas?" Baljeet asked.

Phineas explained about the dream and not remembering anything.

"Huh. Strange," said Baljeet. "But there is one thing that I do not understand. Why do you not simply tell Isabella that you like her?"

Phineas felt his eyes widen and his face go red again. Luckily Buford was distracting everyone by saying, "Come on man. You never tell a girl you like her. It makes you look like an idiot."

"Well, yes, but –"

Weird, Phineas thought. He remembered Buford and Baljeet being in the dream, too. And Candice and Perry and Ferb.

Isabella walked into the back yard while Buford and Baljeet were arguing. "Hey Phineas," she said. "Whatcha doin'?"

"Watching Buford and Baljeet argue," Phineas joked. "Sadly, I think it's the most interesting thing that's gonna happen today."

"What're they arguing about?"

"Oh, er… I don't know?" Even to himself, that sounded completely unconvincing.

Isabella giggled. "Phineas, you're a terrible liar. Spill."

"I really –"

Maybe he was imagining it, but Phineas swore he saw a weird light out the corner of his eye. Either way, Isabella cut him off when she grabbed the front of his shirt and dragged him toward her, so their noses were touching.

"Er… Isabella?"

"You, mister, owe me something from yesterday."

"Wha–"

Phineas was going to ask what she was talking about when Isabella kissed him. And this time, at least he had the sense to kiss her back.

It was a quick kiss, but Isabella looked a bit dizzy afterwards.

"Isabella? You okay?"

Isabella nodded slowly. Her mind was going a bit blank from shock.

Perry, Phineas and Ferb's pet platypus, watched in amusement. Now, as for that Remember-Ray he'd zapped Isabella with so she'd remember that kiss from yesterday… how the heck was he gonna get it back to the OWCA without anybody noticing?

A/N: Well, that's it… kinda cheesy, huh? Oh well. I'm proud of it (especially the last line)

Fern had actually planned it with a reference to Minutemen, so Phineas kisses Isabella and Ferb says "You know she doesn't remember that, right?" "Oh... oops"

I liked my version better