When Professor Marchand, a famous scientist, mysteriously disappears, the commissioner, Juve, immediately suspects Fantomas. Meanwhile, the journalist disguised as Fandor Lefevre, Marchand's assistant, is removed by Fantomas. Commissioner Juve falls into the trap as Fantomas, too, is transformed into Lefevre and they are all found in Rome at a scientific meeting. Fantomas will prevail and stakeholders will gather in his den, and prisoners, it seems, without any possibility of escaping their fate. Accompanied by the music of an organ played by Fantomas.