Rico is happy - his best friend Oskar and his father now live with him in the same building. But then their neighbor Fitzke dies and Rico inherits his stone collection. Even though Oskar thinks they are worthless, Rico disagrees. Sure enough, in the very night after the funeral, someone breaks in to Fitzke's apartment. As they investigate the next day, they find the most precious stone missing! To Rico, the case is clear-cut: They will have to get the stone back. The boys quickly decide to take the train to Prerow where they hope to find the main suspect, Fitzke's foster daughter Julia. Their journey to the Baltic Sea will not only be their biggest adventure but also become the greatest test their friendship has ever had to endure…