Someone is up to mischief in Uncle Fax's garden at night. While Uncle Fax prefers not to take action right away, Fix and Foxi lie in wait and discover not only the sleepwalking Lupo. Everyone is looking forward to Grandma Eusebia's delicious chocolate cake, but it's suddenly gone. The master detectives Fix and Foxi immediately search for traces and are quite surprised at the end. Granny Eusebia actually thought that the surprise party was for her. She is really surprised when she learns who the party is really for and what the surprise cake is made of. When the teacher, Miss Nudelmann, unexpectedly announces a discussion with mom and dad, Pip and Pep have no inkling of anything good. They are doing everything possible to keep their parents from this meeting. But actually Miss Nudelmann only wanted to give praise to the twins.