A green mare makes the fortune of her owner, the horse dealer Haudouin. Shortly after his death, war broke out in 1870. One day, his neighbor Zèphe Maloret denounces Honoré, Haudouin's son, a maverick, to the Prussians. Following this denunciation, their non-commissioned officer enters the Haudouin home and rapes the mother while Honoré is hidden under the bed. The resentment already existing between the Haudouin and Maloret families turns to hatred... A letter recalling the events is lost, which doesn't help matters.