Ships are vanishing from Rome's eastern waters. No storms. No pirates. No survivors. Vessels sail from Alexandria, Rhodes, and Caesarea—and are never seen again. Then the harbour killings begin. A Roman Navarchus drowns in water shallow enough to stand in. Transports burn at anchor, the flames erupting from below. Hulls are holed in the night, sinking without a sound. The Occultum investigate—and find nothing. No witnesses. No enemy. No explanation. For the first time, Rome's secret hunters have no trail to follow. Until a fishing boat drags up something in its nets. Something that shocks even Seneca. Now the Occultum face an enemy unlike any they have encountered—one that strikes from a place Roman soldiers cannot follow. To fight this threat, Lepidus must reveal a secret he has shared with no one—not even Seneca. The Silentium.