This episode page has been compiled from the episode description at the NDR website.
Rumpel are fetching mud for his mud bath, his bucket are filled with so much mud that he spills some as he go back and forth. Meanwhile Pferd discovers some funny looking mud mud stain and right away Detective Wolle appears to investigate. Wolle takes a closer look at the mud stain, he concludes that it must have been brought to were it is since it don't have any legs. Pferd finds 2 more mud stains on the ground. Wolle concludes that it's a mud track and that if they follow it they will discover who made them.
They follow the track to the store, from were they can see a shape around a bath tub at Rumpel's corner. Wolle panics and hides because he are convinced that the shape are a mud monster with a pointy head. Meanwhile Rumpel remembers that he needs is bath brush and goes to fetch it.
Wolle and Pferd observes the mud monster from their hiding place. Pferd notice that suddenly the mud monster changes it's head shape. Wolle thinks that they will have to go in closer to solve the case.
As they come closer they notice that the mud monster starts to sing. They decide to go in even closer. Meanwhile Rumpel prepares for the think he likes the most about taking mud bath, dive into the mud.
Wolle and Pferd reaches the bath tub only to discover that the monster has disappeared. Then Rumpel pops up and Wolle and Pferd are scared and start to run around and ends up running into each other. Wolle are worried about the mud monster knowing their names, but Pferd tells him that the monster are really Rumpel. Wolle declares another case solved