A young inventor is kidnapped to force him to tell the secret of his invention, but he foils his captors thanks to a pen with invisible ink.
| Actor | Role |
|---|---|
 Renée CarlJuliette Michaud | Juliette Michaud |
 René NavarreLe détective Julien Kieffer | Le détective Julien Kieffer |
 Paul MansonEmile Darbois | Emile Darbois |
 Jean DevaldeJean Brémond | Jean Brémond |
| FFernand HerrmannAn Accomplice | An Accomplice |