Employed in a beauty salon, Amédée must undergo a pentothal injection. The dose is too strong; suddenly Amédée reveals the truth to everyone; to clients of the institute; to his cheating wife; to his boss that he robs; to the tax collector; etc. When the effects of the truth serum wear off, everyone returns contentedly to their little swamp.
| Actor | Role |
|---|---|
 RellysAmédée | Amédée |
 Robert ArnouxMareuil | Mareuil |
 Julien CaretteAnge-Louis | Ange-Louis |
 Jeannette BattiJacqueline | Jacqueline |
| CChristine HayrelMonique Castapoul | Monique Castapoul |
 François JouxDoctor | Doctor |
 Marcel PérèsCastapoul | Castapoul |
 André BervilGeorges | Georges |
 Georges TourreilInspector | Inspector |
 Charles LemontierMr. Legros | Mr. Legros |
 Marcel DelaîtreInspector | Inspector |
| PPaul AzaïsPhotographer | Photographer |
 Gaston GabarocheForensic pathologist | Forensic pathologist |
 Jean ClarieuxÉtienne | Étienne |
| RRené WormsFriend | Friend |
| MMadeleine GérômeSaleswoman | Saleswoman |
| PPauline CartonAunt Eugénie | Aunt Eugénie |
 Annette PoivreAmélie | Amélie |
| JJosée Ariel(uncredited) | (uncredited) |
 René LacourtUn ami (uncredited) | Un ami (uncredited) |
 Franck MauriceUn ouvrier de l'institut (uncredited) | Un ouvrier de l'institut (uncredited) |
| MMarcel Portier(uncredited) | (uncredited) |
| LLiliane Robin(uncredited) | (uncredited) |
| CChristian Simon(uncredited) | (uncredited) |
 Roger Vincent(uncredited) | (uncredited) |
 Yvonne YmaUne invitée (uncredited) | Une invitée (uncredited) |