Mary-Kate and Ashley are thrilled about participating in an ice cream-making contest at Sweet Sundaes, an ice cream store in town. Whoever invents the best new flavor will win a free sundae-a-week for a year! The twins stir up a delicious new flavor -- Creamy Orange Choco Chunk-and everyone agrees it's the best ice cream they've ever tasted. But it looks as if the yummy new flavor is a recipe for disaster! First, the ice cream disappears. Then their secret recipe is stolen. Can Mary-Kate and Ashley find the culprit before their sweet success turns sour?