Jean-Louis catches vipers he sells to the laboratories. A trivial incident causes his descent into hell: he forgets to use the pedestrian crossing and the policeman is cross. Who could have believed then where it would lead the unfortunate Jean-Louis to? Two unscrupulous journalists depict him as a monster, who releases vipers in town. Because of a hold up, the city is looking for a scapegoat, and this poor lad looks the part too much. Although the superintendent insists there's really nothing against him, Jean-Louis becomes paranoiac and hides in shady places. He leaves his girlfriend, meets a hooker and a shifty aging man...