Some news from France: The third book in Les aventures de Johnny Dixon will be Le secret de la salle souterraine to be published in February 2005.
We realize that The Secret of the Underground Room is actually the eighth Johnny Dixon book in the series but it has jumped up to book three in the French series. Lalex, the illustrator of the French books, notes on her website that the fourth book will probably be The Spell of the Sorcerer's Skull but no release date has been set.