In an aero-naval base, a marine engineer who was about to deliver the name of a redoubtable spy is murdered. Shortly afterwards three different men appear on the crime scene, each of them claiming to be Monsieur Sylvain, the expected sleuth. But which of the three investigators is actually Sylvain? And what about this delightful young lady who arouses one of the police inspectors? Couldn't she be the murderous spy?
| Actor | Role |
|---|---|
 Frank VillardAncelin | Ancelin |
 Simone RenantFrançoise Dastier | Françoise Dastier |
 Jean ChevrierChantenay | Chantenay |
 Jean MarchatMorgat | Morgat |
 Marcelle PrainceThe marquise | The marquise |
 André BervilThe killer | The killer |
| MMarcel RaineCommander Dartois | Commander Dartois |
 Paul AmiotThe colonel | The colonel |
 Claude NollierNot listed | Not listed |
| SSuzanne BaraNot listed | Not listed |
| RRoger BontempsNot listed | Not listed |
 Max DoriaNot listed | Not listed |
| JJacques MattlerNot listed | Not listed |
| JJacques MullerNot listed | Not listed |
| RRoger CoiraultNot listed | Not listed |
| MMaud LamyNot listed | Not listed |
 Philippe DumatInspector | Inspector |