Fix and Foxi are thrilled because Professor Knox's popcorn-producing plant promises to be the hit at the flea market. But the joy doesn't last long, because Wurst-Maxe is angry with the competition and steals the plant together with grandma's car and Schnucki. Professor Knox wants to explore the deep sea and takes Fix and Foxi and Lupinchen on a trip. When he and his diving bell are separated from the boat and sink into the sea, the friends have to come up with something quickly. Professor Knox presents his new servant robots at a dinner party. Lupo is of course enthusiastic and dreams of always being served. Finally, he fakes an accident to make his dream come true. Neighbor Breitmaul wants to cut down the tree in which the twins have built a tree house. And Pip and Pep see this as an official declaration of war.