(Chelo Holmes and the Secret of the Invisible). Chelo Holmes and her helper, Huan Shon, receive the unexpected visit of King Leónidas, who is worried about the disappearance of the court’s wise man, Doctor Fenron. Chelo and her helper have a new investigation to undertake, but they must start by visiting the royal palace again, most especially the laboratories of Doctor Fenron, where they find a game of clues that seems impossible to solve.
