Katja has suddenly disappeared. Nobody knows where it is. Together with TKKG you search for traces, interview witnesses and find out the riddle. What role does Peter, the nasty tutor, play? Why is Sandra silent? Is Barbara Dupont really as clueless as she pretends to be? Only those who find the secret message and decrypt the code together with Tim, Karl, Klößchen and Gaby have a chance to solve the case.