Findus is feeling bored and wishes to celebrate his birthday again. However, they have already celebrated it three times this year. Then, Findus remembers that he came to Pettersson in a box. So, they could celebrate the Findus-in-a-box birthday! The chickens are excited about this idea. Pettersson is persuaded and even promises to make his famous pancake cake. But he can't find the flour, and he can't buy any more because his bike has a flat tire, and the key to the carpenter's shed is missing.

Once they gather everything for the cake, their neighbor Gustavson brings bad news: a fox has been spotted again. The neighbor wants to deal with the chicken thief soon. Pettersson and Findus think that shooting him is too extreme - just scaring him will do. But will their plan actually scare the fox away?