Severinus is in charge of the infirmary, where he works as the abbey’s herbalist and doctor, ministering to the sick and dispensing medicine. He quickly strikes up a friendship with William, with whom he shares a passionate intellectual curiosity. When he finds a mysterious Arabic manuscript in the infirmary’s library, he immediately informs William, but by the time William arrives at the infirmary to see the book, it is too late: Severinus is found dead and the forbidden book is stolen shortly afterwards.