Young Adso of Melk leaves the ranks of his father, a powerful warlord, and joins William of Baskerville, a Franciscan monk who heads to an abbey in northern Italy to participate in a theological debate.

After another outrageous event occurs, William's investigation leads him and his apprentice Adso to the doors of the mysterious library, where everyone but the librarians are forbidden to enter. Meanwhile, the inquisitor Bernardo Gui, Pope John's ambassador, brings the wrath of his fanaticism to anyone who cross his path.