Potato gremlins appear all over town when Phineas and Ferb clone a potato chip from Buford and it mixes with his DNA; Doofenshmirtz tries to summon the Spartan army with his historical army retrieve-inator.

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. 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."