Youngmee's Aunt Christie opens a confectionery store adjacent to Littlest Pet Shop, and the pets meet pet Buttercream Sunday, a hyperactive rabbit, who invites them to overindulge themselves on the sugar-filled treats located in Christie's pantry.
Zoe, temporarily bandaged due to an embarrassing pimple on her nose, asks Penny Ling to pass along her romantic feelings to her crush, Digby, during his stay at the day camp. Meanwhile, Russell hides in Blythe's backpack, wanting to pursue an education, but gets lost within the corridors of her high school.
Surrounded by guilt, the pets try to prove Blythe's innocence after she is accused of sending Aunt Cristie's truck careening down the street while meeting Buttercream's alley cat friend, Sugar Sprinkles.
Blythe enlists the pets to retrieve her new favorite necklace that fell inside a vat of batter used for filling a huge cupcake order with Youngmee. This proves difficult for them, when they discover the order was placed by Fisher Bisket for his twin daughter's "quarter-birthday" party.
Russell, Zoe, and Vinnie, along with Buttercream, try to retrieve a recipe stolen from Blythe by the Biskits, who plan to use it for a baking competition hosted at Blythe's school. All the while, Vinnie has a vision of cakes occupying the world.