The 4½ Friends consist of three boys, one girl, and a dog. Kalle, the founder and leader of the detective agency "Kalle and Co," the twin siblings Steffi and Karsten, Friedel, and their dog, the Beautiful One, get involved in various adventures as they try to solve mysteries and strange cases. Friedel, a member of the "Kalle and Co" detective agency, is in love with the strict biology teacher, Ms. Schulte-Stratmann. However, she suddenly starts to behave strangely. What could be behind this behavior? And is it just a coincidence that a robbery recently took place at their local bank? Could she be involved in this case? When Ms. Schulte-Stratmann goes missing, the "Kalle and Co" agency decides to take action.