The 13-part children's mystery series based on the bestselling novel by Tonke Dragt. "The Secret of the Seventh Way" is not only cult, it is one of the most beautiful and exciting children's series of all time. Every day, teacher Franz van der Steg tells his pupils fantastic stories. But one day, one of these stories becomes reality: Franz and his pupils become involved in a mysterious plot to hide a treasure in Count Grauenstein's castle. The count is holding his nephew Geert-Jan prisoner there, to whom the treasure belongs. Franz manages to sneak into the castle as Geert-Jan's private tutor. Bit by bit, a centuries-old prophecy is fulfilled... Marjan, Kees, Joke, Els and all their classmates are enthusiastic about their teacher Frans van der Steg, who often tells exciting, self-invented stories. One day, however, something strange happens: a mysterious letter signed "GrGr" is blown to Frans by a storm.