Falco and his family attend a dinner party in Alexandria, Egypt, hosted by his mother's brother Fulvius and his partner Cassius, to which the Serapaeion Chief Librarian, Theon, is invited.

More deaths soon follow: an old scholar, Nibytas, is found dead in the Library of Alexandria, while a student, Heras, is devoured by a crocodile in Philadelphion's care, further compounding the difficulty of Falco's investigations.

A deadly chase through the streets of Alexandria ending at the top of the Pharos soon reveals more: the Director was stealing library scrolls for resale back to Rome; the intermediaries being none other than Falco's uncle and father, Fulvius and Geminus.

Fearful of being found out, Philetus starts a fire in the library, but Helena and the students manage to douse the blaze; he is eventually forced to relinquish his post as Director.

Falco discovers a love triangle between Philadelphion and a lawyer named Nicanor, but both men reconcile and take turns to "share" the woman.