This is probably the first film that has ever been made on speleology in China where the sport is not wellknown and is therefore not practised like it is in Europe. The reason for this is an old belief: the grottoes are the homes of good spirits and they should be left in peace. The French expedition explores the "Green Dragon" grotto, the largest in the country, situated in the geografic centre of China, and tries to discover the secrets of it tumultous waters.