The boys decide to put on a traditional family Christmas special featuring their family, friends and a few very special guests, including Grammy winning recording artist Kelly Clarkson (playing herself). The episode features three new holiday songs - Isabella's "Let it Snow", a Buford and Baljeet rendition of "Good King Wenscelas" and the whole gang singing "We Wish You a Merry Christmas".

Meap's world is put in danger and the boys try to help him save the universe when they travel to Seattle. Meanwhile, Doofenshmirtz visits former nemesis Peter the Panda.

Agent P's fate is finally revealed in the action-packed finale of the two-part television special that left Phineas, Ferb and the gang hanging...literally off an unchartered gorge and Candace frantic over a phone call with Jeremy that left their relationship status in limbo. Now, with Agent P nowhere in sight, Dr. Doofenshmirtz and Major Monogram square off against evil Carl who controls a set of familiar-looking robots to take over the OWCA, in one of the biggest battles yet.

After discovering that a strange planet is hurtling directly towards Danville, Phineas and Ferb set out to avert a disaster, while Buford looks forward to making contact with its alien race. Meanwhile, Dr. Doofenshmirtz hopes to steal the world's largest ball of twine.