Zeno's mother is found unconscious and drooling, and Maia is sent to nurse her – only to end up with a black eye when the woman, Pullia, wakes up.

Back in Ostia, the local vigiles chief, Brunnus, suggests that Falco talk to an expert on piracy — a naval officer named Caninus.

Falco's sleuthwork also reveal a darker side to law enforcement in Ostia — the vigiles are seen as heavy-handed and not trustworthy, and so fire fighting and security work is done mostly by members of the local builders' guild, headed by a rich building contractor named Privatus.

More note tablets by Diocles turn up, proving that he had contact with someone who had engaged in piracy, mentioning the name of Lygon — Zeno's uncle, and possibly one of Damagoras' henchmen.

Suddenly, Holconius and Mutatus arrive in Ostia, with what seems to be a large chest full of cash in order to ransom back Diocles on Helena's advice.

Much later, however, Falco catches sight of the alleged kidnappers with the ransom chest, and tails them to a military dock, where they are planning to board a liburna, but is spotted and attacked.

As usual, things get out of hand once Rhodope identifies a suspect for Theopomous' death at his wake, sparking a gang war which results in a three-way melee between the Illyrians, Cilicians and the vigiles.

Falco, his family as well as Petro' manage to rescue Rhodope from the fight and take refuge in a mausoleum, where she finally reveals that during her captivity she was drugged (possibly by Pullia) and held in a sacrificial vault in a temple.

After being rescued along with Petro and the rest, Falco follows Mutatus into a temple to Cybele to meet with Diocles' supposed captors, where he bumps into Fulvius, who reveals that he works for the Navy as an intelligence gatherer, and that he has been watching Caninus, who is the actual "Illyrian" — this is soon proven when they hear Caninus demanding the ransom money from Mutatus, before killing him.

Falco finally figures out what the strange grid pattern in Deiocles' possession was — it's a map, and shows that Diocles may have been working on the old vigiles station prior to disappearing.