When Isabella writes a letter about her feelings for Phineas and accidentally sends it, she and the Fireside Girls work to get it back. Meanwhile, Doofenshmirtz invents an Unretrograde-inator to reverse his bad luck.
Tropes:
- Alternate Catchphrase Inflection: Isabella asks Phineas what he is doing with a nervous stammer, since she doesn't want Phineas to read her letter.
- Catchphrase Interruptus: When Phineas sees a spork, he calls it "a perfect fusion of aesthetics and utility. It's like a little work of art." Then the Ethereal Choir starts and Phineas says, "Ferb, I—" but before he can say the other six words, Candace interrupts to ask him what they are doing.
- A Day in the Limelight: For Isabella and the Fireside Girls.
- Freeze-Frame Bonus: Upon close inspection, Isabella's letter has the "Lorem ipsum" filter.
- I Want You to Meet an Old Friend of Mine: This episode reunites Carol Kane (Nana Shapiro) with Marilu Henner (Nana's unnamed friend) who were in the cast of Taxi.
- If I Had a Nickel...: Dr. Doofenshmirtz puts a coin-operated self-destruct button on his Unretrograde-inator because he thought to himself that morning "If only I had a nickel for every time [Perry the Platypus] hit my self destruct button..." Unfortunately for him, Perry has a nickel stashed under his hat.
- Irrevocable Message: Isabella tries to get back a love letter she hastily wrote for Phineas.
- The Unreveal: Whatever was written in Isabella's letter is never shown openly.
- The Voiceless: Adyson is the only Fireside Girl without speaking lines.
