Pierre Leroux, an ordinary carter from the Beaugency area whose modest life centers entirely around his horses, is arrested and accused of murder on thin evidence. The case is prosecuted in Orléans by Monsieur Desalleux, an ambitious deputy public prosecutor obsessed with oratorical fame. Driven by vanity and a determination to impress high society, Desalleux delivers a theatrical closing argument that sways the jury into sentencing the carter to death. Six weeks later, Leroux is sent to the guillotine and executed before a crowd.
Months after the execution, while Desalleux prepares another capital case late into the night, he encounters a terrifying apparition: the severed, bleeding head of Leroux hopping toward him across his desk. The prosecutor faints in terror, awakening in a pool of blood that observers mistake for a hemorrhage. Reassured by a materialistic doctor who attributes the incident to mental strain, Desalleux resumes a lighter schedule and eventually contracts an advantageous marriage with an elegant young woman.
On the wedding night, Desalleux enters the bridal bedchamber and discovers the spectral head lying on the pillow beside his sleeping bride. When he attempts to grab the phantom, the head bites him. In a blind frenzy, Desalleux seizes a heavy iron bar from the fireplace and repeatedly strikes at the elusive intruder. After the ghost vanishes, he finds the bed soaked in blood and his wife completely unresponsive to his embraces. When daylight breaks, he realizes with horror that his blows had fatally struck his bride in the temple.
Overwhelmed by madness, Desalleux bursts into uncontrollable laughter and drags his mother-in-law to view the corpse. Arrested immediately and confined to the very cell Leroux had once occupied, the former orator is declared insane and placed in an asylum, where he spends his remaining days imitating a tightrope walker while an Orléans bookseller sells multiple editions of his speeches.