Marcus Attilius Primus arrives in the Bay of Naples from Rome to take charge as "aquarius" (hydraulic engineer) of the Aqua Augusta, the aqueduct that supplies water to the towns in the region encompassing the Bay of Naples and Mount Vesuvius. The nine important towns are, in sequential order, Pompeii, Nola, Acerrae, Atella, Napoli, Puteoli, Cumae, Baiae, and Misenum. Attilius' predecessor, Exomnius, has mysteriously vanished as the springs that flow through the aqueduct begin to fail, lowering the supply of water available to the region's reservoir. Attilius is unpopular among the workers, particularly Corax, who resents the young foreigner giving him orders. Attilius's concerns about the water are heightened when he is summoned by a young, wealthy woman named Corelia to investigate water that apparently killed her father's prized fish. Corelia's father is the former slave and land speculator Numerius Popidius Ampliatus, who came to fortune after rebuilding Pompeii from a past earthquake. Ampliatus feeds the slave he deems responsible for the fish's death, to eels for his own amusement. Attilius realizes that, unusually, sulfur poisoned the water.