In the Norwegian city of Bergen, lives a perfectly ordinary family: mom, dad, six-year-old Martin, and his older sister, Matilda. But everything changes, and life suddenly becomes filled with exciting events when Grandpa Oscar, whom the children have never seen before, comes to visit. It's not for nothing that Oscar is nicknamed Chocolate Grandpa, because he has a terrible sweet tooth and can't live without candy and chocolate.

First, Martin and Matilda, accompanied by Grandpa, have to contend with the machinations of the mischievous Paulsen sisters, who dream of disrupting the annual city sweet fair. And then they travel through time, meet Vikings, and search for a stolen chest containing a magical artifact that grants wishes.

After all, where Chocolate Grandpa is, there are always adventures and magic!