Isabella's favorite necklace is hit by Dr. Doofenshmirtz's CURSED Make-Bigger-inator, which now causes things hit by it to grow to 50 feet tall (Why 50 feet? I simply don't know.) from midnight to sunrise.
The whole curse thing started right after the episode "Out of Toon", when those Pacific islanders that cursed the storyboard hopped onto Doofenshmirtz Evil Incorporated and cursed the Make-Bigger-inator before they summoned a flying canoe and headed back to the islands. In the present, at night, Isabella spills her bedside water glass on her favorite necklace and puts it on the windowsill to dry overnight. Meanwhile, Perry came to D. E. Inc. and during the late fight, he accidentally hits the switch. Its course is slightly adjusted and it hits Isabella's necklace. She puts it on the next morning, but the chain won't open after she does, so she can't get it off. She visits Phineas and Ferb and asks, "Watcha doin'?" Phineas asks where she got the necklace, and she replies she got it for her birthday last year, and goes home. A little before midnight, she wakes up and goes outside. Then she rapidly grows to 50 feet! Phineas and Ferb come outside and ask what happened. They notice the necklace is glowing. At dawn Isabella returns to normal. Baljeet examines it and concludes it's cursed, but doesn't know why. Ferb suggests asking Daniel Radcliffe, but Baljeet responds that he is "just an actor" and "what does he know". Daniel, who was nearby, responded by saying heard everything Baljeet said and asks Phineas that isn't a cursed necklace too Harry Potter and the Half-Blood Prince, to which he replies "Why yes. Yes it is." They finally manage to get the cursed necklace off, but Candace finds it and puts it on...
Read the sequel, Return of the 50 Foot Sister.
Perry the Platypus
Too Young Line
Daniel Radcliffe: "Isn't it a little too Harry Potter and the Half-Blood Prince to have a cursed necklace?"
Phineas: "Why yes. Yes it is."
Baljeet: "According to my studies, this necklace is cursed."
Baljeet: "I do not know."
Ferb: "Maybe we should ask Daniel Radcliffe."
Baljeet: "He is just an actor! What does he know!?"
Daniel Radcliffe: "Um, Hello! I can hear every word you're saying!"
Isabella: "Hi Phineas. Hi Ferb. Watcha doin'?"
Phineas: "We're trying to come up with an idea. Rollercoaster... no. Singer... no. That's it, Ferb! I know- Say, where'd you get that necklace?"
Isabella: "Oh, this? I got it for my birthday last year."