The means used by foreign spy services to obtain the trade secret of a French invention.
| Actor | Role |
|---|---|
 Claude RolletYves Rubin | Yves Rubin |
 Danielle GodetSonia | Sonia |
 Paul PréboistLéon Prades | Léon Prades |
 Jacques GallandRobert Alexandre | Robert Alexandre |
 Henri LambertDabillaud | Dabillaud |
 Daniel PrévostMario | Mario |
| MMichèle CheminJanine | Janine |
 Christine AurelIrène | Irène |
 Dennis BerryJean-Marc | Jean-Marc |
 André RouyerPierre | Pierre |
 Jean RupertThe man on the train | The man on the train |
| JJean PerrinThe representative | The representative |
 Paul PavelW (the spy) | W (the spy) |