Twelve-year old Kosta, a little boy of an overactive imagination, makes friends with equally sensitive eleven-year old Blanka. Fantasy leads the two children to the forgotten attic in the house of Blanka's parents. For them, this is the forbidden "thirteenth chamber," and to Kosta, an old glass vase becomes a magic ball with the help of which he can play his favorite play "on fate". The children observe the adults and unconsciously sense that something has gone wrong in Blanka's family. Her dad is a physician and her mother is not happy with him, still recollecting her former wooer Petr who left for India upon his graduation.