Venus in Copper

Venus in Copper is a 1991 historical mystery crime novel by Lindsey Davis and the third book of the Marcus Didius Falco Mysteries series. Set in Rome during AD 71, just after the year of the four emperors, the novel stars Marcus Didius Falco, informer and imperial agent. The copper of the title refers to a simple copper signet ring featuring a portrait of Venus, worn by the suspect Severina Zotica. That Venus was the goddess of love hints at the motives for some of the murders perpetrated by the suspect: revenge out of unrequited love.
Plot summary.
The story begins in Rome during late spring, AD 71. Falco is in the Latumiae Prison, accused by the spy Anacrites of having stolen lead ingots which were property of the State (Shadows in Bronze). Bailed out by his mother, Falco is heading across the city to visit Helena Justina when he is beaten up by his landlord's bullyboys for defaulting on his rent—despite having been bailed out by none other than Helena Justina. Marcus decides to resume working as an independent, despite the fact that this means he is unlikely to be able to earn enough money to buy himself into a higher rank so that he can marry Helena.
Luck seems to smile down on Falco. A slave, Hyacinthus arrives at Falco's apartment in Fountain Court to ask him to assist the Hortensii, a trio of "nouveau riche" freedmen. Hyacinthus also recommends a real estate agent to Falco named Cossus, who eventually gets Falco a new home. Falco agrees to visit the Hortensii, who live on the Pincian Hill. There, Sabina Pollia informs him that all of the Hortensii (Crepito, Felix, Novus and their wives) live together in the one house. Novus is the only one currently unwed and he is due to marry Severina Zotica, but Sabina Pollia informs Falco that she believes Severina plans to murder Novus. Falco chooses to investigate Sabina's claims. At the same time he also begins to hunt for a new apartment in which to live.
During the course of the investigation, Falco is once more arrested and imprisoned in the Latumiae by Anacrites, who then brings forth his charges regarding the lead ingots (from the two novels preceding "Venus in Copper") to Titus but Falco persuades Titus to free him, provided he repays whatever is owed for the lead to Emperor Vespasian, and is asked to undertake more work for the Palace. Falco agrees to be available provided he is paid for previous missions that have already been completed. This is agreed to by Titus, who then presents Falco with a huge turbot, which vexes Falco as he not only has to investigate Severina—but to find a suitable way of cooking the turbot as well! The arrival of the turbot becomes the cause of an impromptu party amongst friends and family of the Didii. Helena arrives, complete with baggage with which to move in with Falco, only to discover that she had not been invited to the party. Distraught, she attempts to leave, but is prevented by the arrival of another guest, who turns out to be none other than Titus and the Praetorian Guards, who have arrived to sample the fish. At the end of the party, Helena chooses to stay on with Falco.
Returning to the house of the Hortensii, Falco discovers that Novus is dead in the privy after a banquet. He has been poisoned. Severina comes under suspicion, but Falco can find no real clue. Sabina wants to pay him off and considers him a failure, when the news arrives that Viridovix, the Hortensii's Gaulish cook, is also dead. He too was poisoned. Continuing to investigate, Falco is beaten up badly by thugs working for Appius Priscillus, a rival of the Hortensii, but is rescued and nursed back to health by Helena in their new apartment. When he finally recovers, he continues to investigate but returns only to see the apartment block in which they are living collapse. Believing Helena to be inside, Falco and others begin to dig. Helena arrives just as all hope seems lost. By a freak accident, Helena and Falco run into Cossus after helping to search for other survivors in the rubble, and after interrogating Cossus—now revealed to be an operative for the Hortensii—they discover that the Hortensii owned Falco's apartment block. Cossus is lynched and crucified by an angry mob.
All at once, Falco and Helena conclude that Severina poisoned Novus as revenge because a building owned by Novus had previously collapsed, killing her lover, and had (as Novus' representative) tried to demolish Falco's home to kill Helena out of romantic jealousy. Falco confronts Priscillus, the Hortensii women and Severina Zotica. Priscillus and the Hortensii women are revealed to have been planning to kill Novus (who was threatening to evict the other freedmen from the Hortensii business), but were beaten to him by Severina. Falco forces Priscillus to leave Rome, and blackmails the Hortensii into buying his silence by "donating" to a charity set up by Helena. As for Severina, Falco is unable to prove anything but Severina nevertheless doesn't go unpunished and is herself blackmailed into marriage by an inquisitive public servant who has managed to obtain evidence of her past misdeeds.
Left with no home, Falco and Helena move back into Fountain Court.