Set in France in the 1890s, it shows the capture after a trail of rapes and murders of a possibly deranged ex-soldier, based on the historical Joseph Vacher, and how he is befriended by an ambitious judge who leads him into incriminating himself.

Ex-sergeant Bouvier, expelled from the army for fits of violence, shoots at Louise when she rejects him and then puts his last two bullets in his own head.

Rejecting civil society on his release, he wanders the countryside raping and murdering isolated teenage children.

His crimes are followed closely by Rousseau, a provincial judge, and when Bouvier enters his jurisdiction he is arrested.

When Bouvier is condemned, Rousseau's working-class mistress Rose joins the strikers in the town factory.