Fearing the theft of an important secret formula, the scientist Claude Amory asks for help from Monsieur Préval, director of the Sûreté. But when Amory is mysteriously poisoned inside his own home, the detective realizes the case is more serious than he had imagined and decides to investigate each of the suspects.
| Actor | Role |
|---|---|
 René AlexandrePréval | Préval |
| HHarry ArbellAntoine | Antoine |
 Maxime DesjardinsClaude Amory | Claude Amory |
 Gaston DuprayGaston de Ravennes | Gaston de Ravennes |
 Alice FieldLucie Stenay | Lucie Stenay |
| MMaurice VarnyRichard Stenay | Richard Stenay |
 Danielle DarrieuxHenriette Stenay | Henriette Stenay |
 Marcel VibertDr. Carelli | Dr. Carelli |
| AAndré LaurentRaynor | Raynor |
| IIsabelle AndersonMarthe | Marthe |
| JJean LaurentDr. Dernault | Dr. Dernault |