Recurring characters include across-the-street neighbor Isabella Garcia-Shapiro, the boys' mom Linda Flynn-Fletcher, the boys' dad Lawrence Fletcher, Perry's boss Major Monogram, Carl the Intern, Candace's crush Jeremy Johnson, Baljeet Tjinder, Buford Van Stomm, Candace's best friend Stacy Hirano, and many more.
When the boys accidentally knock a spacecraft out of the air with a remote-controlled baseball, Candace discovers an alien named Meap, who she initially believes is a plush toy that had been "robotized" by her brothers.
Meanwhile, when Dr. Doofenshmirtz tries to retrieve a balloon he had treated as a friend in his childhood using static electricity, he and Perry are launched into the crossfire of the battle with Mitch.
Guest stars: David Mitchell as Mitch, Lorenzo Lamas as Meap, Don LaFontaine as Opening Narrator After encountering them in the future, an older version of Candace decides to steal Phineas and Ferb's time machine and go back in time to the day they built a rollercoaster so she can help the present Candace catch them in the act.
In a side story of the previous episode, Isabella and her Fireside Girls troop try to retrieve a rare variety of tree sap for Phineas and Ferb's bubble project from an abandoned amusement park.
After Phineas, Ferb and their friends help decorate the city to celebrate the arrival of Santa Claus, Dr. Doofenshmirtz, after finally finding a reason to hate Christmas, uses his Naughty-inator to try to ruin the holiday for everyone.
In the second part, Phineas and Ferb help Candace get rid of a lava necklace of bad luck, and Perry and Doofenshmirtz get stranded on an island.
Meanwhile, Dr. Doofenshmirtz takes a father trip to Tokyo, Japan with Vanessa, but sets out with Perry and Major Monogram to find her when she joins Phineas, Ferb and the others.
Phineas and Ferb head to the Tri-State area's annual sci-fi/fantasy convention to meet their hero, special effects guru Clive Addison.