Franciscan friar William of Baskerville and his novice, Adso of Melk, arrive at a Benedictine abbey in Northern Italy during the early 14th century. The abbey is shrouded in mystery as it faces the unsettling aftermath of a young illuminator's apparent suicide just before a significant theological Church conference. With a reputation for his sharp deductive reasoning, William approaches the anxious Abbot and receives permission to delve into the circumstances surrounding the death. As days unfold, the situation worsens when more unusual fatalities arise.
Their investigation introduces them to Salvatore, a hunchback who struggles to communicate coherently in various tongues, alongside his protector, Remigio da Varagine. William discerns from Salvatore’s mention of a penitenziagite that he might have previously belonged to a heretical sect, raising suspicions about their connection to the recent killings. Meanwhile, Adso engages with a peasant girl who has cleverly infiltrated the abbey, trading sexual favors for food and, in the process, experiences a pivotal loss of innocence.
Yearning to prevent any misconduct allegations, William and Adso explore a concealed library within the abbey’s forbidden main tower. William uncovers that it boasts "one of the greatest libraries in all Christendom," filled with lost works from Classical thinkers like Aristotle. This knowledge is deliberately hidden, as it's deemed incompatible with Christian teachings. William also concludes that all previous victims had perused the only extant copy of Aristotle’s Second Book of Poetics.
Their inquiries are abruptly interrupted by the arrival of Bernardo Gui, an Inquisition representative summoned for the conference who is eager to bring those he suspects of wrongdoing to justice. Having clashed with William previously, Gui dismisses alternative theories. During a chaotic moment, Salvatore and the girl get into a struggle over a black cockerel amidst the presence of a black cat. Gui seizes this opportunity as undeniable evidence of their supposed pact with Satan and forcibly extracts a false confession from Salvatore. Both Salvatore and Remigio, alongside the girl, face persecution in a tribunal overseen by Gui, who coerces the Abbot into supporting his heresy claim. William, although forced to join the panel of judges, challenges the accusations by noting that the real murderer must have been able to read Greek—a skill beyond Remigio.
Following a series of intense events, when the head librarian dies like the others, William and Adso ascend to the forbidden library, confronting Jorge, the abbey's oldest inhabitant, who possesses the fatal book that discusses comedy and its potential as a teaching tool. Jorge, believing humor to be a tool of the Devil, has poisoned the pages to prevent the dissemination of what he perceives as dangerous ideas. In a desperate turn, Jorge ignites a candle that sets the library ablaze. William urgently instructs Adso to escape while he futilely attempts to salvage valuable texts, ultimately losing the Poetics, Jorge, and the entire library to the flames.
Tragedy befalls Salvatore and Remigio, who are executed by fire. The girl, marked for a similar fate, is liberated by local peasants amidst the chaos ignited by the library fire, who also seize the opportunity to retaliate against Gui. In his desperate escape, Gui meets his end when his wagon is toppled over a cliff by the enraged villagers. As the dust settles, William and Adso leave the abbey, yet not without a poignant moment when Adso is momentarily halted by the girl, silently urging him to remain. Despite the temptation, Adso continues with William. In a reflective narration later in life, Adso contemplates his choices, stating that he has never regretted his decision, having gained profound wisdom from William. He acknowledges the girl as the singular earthly love of his existence, lamentably admitting that he never came to learn her name.
