Tartini's Key Tartinijev ključ

The action takes place in Piran where three children meet by chance. Mario is a local living with his grandmother, Robert, who comes from a family of a lower social status, is in Piran with his friends from his summer camp and Barbara is from a well-situated family but her parents are divorced. A stray text message sent to a wrong (Barbara’s) number sets off a chain of events that take our heroes through exciting adventures by means of various riddles connected to medieval Piran.