In Last Seen in Massilia, the seventh volume in the Roma Sub Rosa series of novels and short story collections relating the adventures of Gordianus the Finder, a Roman private detective, set in the final decades of the Roman Republic, Gordianus is at Massilia (the modern-day Marseille). The year is 49 B.C., and the Roman Republic is torn by civil war. Massilia is loyal to Pompey and is being besieged by the forces of Julius Caesar, Pompey’s rival.
Gordianus, accompanied by his son-in-law, the ex-slave Davus, is seeking information about his adopted son Meto, who has been rumored killed in Massilia. Complicating the situation, Meto was publicly a turncoat, having abandoned Caesar for Pompey. Secretly, however, he was Caesar’s spy. In asking questions, Gordianus must gauge whether his informant is aware of Meto’s true status. If Meto was still alive, Gordianus might doom him by an ill-chosen question.
Through a lucky turn of events, Gordianus and Davus manage to enter the city, where they are befriended by Hieronymous, the doomed scapegoat whose self-sacrifice might save Massilia from its horrible fate. Hieronymous provides Gordianus (and the reader) a convenient way to learn all about the customs of Massilia.
While seeking news about Meto, Gordianus witnesses the fall of a young woman. Was it murder or suicide? Even amidst the hardships of the siege, Gordianus must resolve this mystery, for knowing the truth means more to him than anything, even, as he admits, when there’s no point to it. He does manage to learn the truth about the fall, as well as Meto’s fate. But he also acquires insights into Meto’s character which he wishes he had not. In the end, Gordianus leaves Massilia in possession of the truth, but considerably more unhappy than when he arrived.