Knock, a retired crook-turned-doctor, arrives in the small town of Saint Maurice. He intends to implement a scheme to make him rich by persuading the villagers that healthy people are simply people who don't realise they're unwell.

Doctor Knock is a former thug who has become a doctor and arrives in the small village of Saint-Maurice to make his fortune according to a particular method. It will make the villagers believe that they are not as healthy as they might think. It is thus that he will find in each one an imaginary symptom, or not, and thus will be able to exercise his profession lucratively. Under his seductive looks and after gaining the confidence of the village, Knock is on the verge of achieving his ends. But his past catches up with him and an old acquaintance disrupts the doctor's plans.