When Helena gets an invitation to a private dinner with Titus, she pleads that Falco stay by her side on the same day, but he instead decides to see a client in Veii — who unfortunately turns out to be a widow more intent on pleasure than business.

Romantically depressed, Falco goes over to the Palatine to be personally briefed by the emperor Vespasian on his latest assignment — broker peace between Rome and the Celtic tribes of Germany (whose leaders are thought to be Veleda, a priestess and Julius Civilis, a local strongman), locate a missing military officer named Munius Lupercus, and deliver a new standard in the form of a two-foot long human hand, cast in iron, to the 14th Gemina at Moguntiacum — the last actually being a pretext for Falco to investigate them, given that the 14th's loyalty is held in doubt.

Falco's trip is marked by a number of misadventures — poor food and even poorer wine, unscrupulous souvenir sellers and cramped conditions, as well as murder.

Running out of leads, Falco finally tries to make enquiries with the camp prefect of the 14th Legion, but accidentally lets it slip that he was part of the infamous 2nd Augusta.

Just as things begin to look bleak, however, Justinus rides in and speaks with Veleda in Celtic, offering himself up as a hostage in return for the safe passage of Falco and his team back to civilisation.

She asks Falco and Helvetius to use a galley captured from Petillius Cerialis (now decrepit from neglect) to escape so as to throw off the tribesmen's suspicion — she must not be seen aiding the Romans.

Unfortunately, the galley is in poor shape and Falco and the men are soon shipwrecked in the lands of the Tencteri, a staunchly anti-Roman tribe, where they encounter the 14th Gemina's legate, Florius Gracilis, hunting for aurochs with the Gauls of Lugdunum, who then kill Helvetius.