As soon as he arrives in Rome with his faithful assistant Archie Goodwin, the famous American investigator, Nero Wolfe, is contacted by his first client: a woman asks to find a boarder in the hotel where she works, disappeared for days

Recruited as a chaperone at a reception for mothers-girls, Archie Goodwin assists helplessly with the death of one of the two young escorts, Lucia, poisoned with arsenic. The police are sure it is suicide, but Archie is convinced of the opposite, and initially Nero Wolfe suspects the victim's ex-boyfriend, who had been abandoned to the news of the pregnancy and later lost the child.

Yu Lan, a young peddler vendor, describes to Nero Wolfe a woman kidnapped in a car: she had a pin with letters C and S and a faith. Without taking it too seriously, the investigator invites Archie Goodwin to deepen, but before the assistant can do it Yu is hit by the same car of the kidnapping and ends up in a coma.

An accountant and his principal contact Nero Wolfe: the first one accuses the charming Lara Fox of the theft of the salaries of a troupe of Carosello; the second defends the actress because he loves her. Not only is Lara exonerated by Wolfe, but she proposes herself as a client: her father and four others during the war entered into the "Covenant of the Six" with an English lord, Clivers, to help him escape from a prison. Freedom to them, a rich reward to them. The man never honored the debt: Wolfe's task is to help the survivors and their heirs to collect the sum until Clivers is in Rome. When Sordillo, another member of the Six in town to talk to Wolfe, is shot dead, Wolfe suspects that Clivers has something to do with it. Graziani, meanwhile, has found the wages of the troupe in Lara's car and intends to arrest her, but Wolfe hides the actress at home and so saves her. Then with the help of Archie Goodwin organizes a close confrontation with the lord, which surprisingly claims to have already paid the debt years earlier with another member of the Six, Meduni. Which, however, has long since disappeared. The version of Clivers is credible, even more so when Archie explains to Wolfe that the last survivor of the Six, a security guard named Sgroi, was strangely .

The immediate intervention of dr. Malaspina, who gave him an antidote: the chess genius Valerian died poisoned in the middle of an exhibition with which he would pay the transfer to America with his girlfriend Rossana Ferri. The police nailed the girl's father, the entrepreneur Matteo Ferri, guilty of having passed to the young the toxic drink, but it is precisely the daughter to hire Nero Wolfe, convinced of his innocence. To the detriment of Ferri, who in public had shown to dislike the relationship between Valerian and her daughter, there is the motive and the dynamics of the murder; but his wife Esther and the lawyer Guastalla say they possess a detail that will exonerate the accused. Wolfe is inspired by the investigation of Graziani to understand that Ferri was framed: among the exhibitors, few knew Valerian, while everyone was in contact with the entrepreneur. Suspicion of Guastalla, that Rossana accuses of having a story with her mother, but when Archie goes to the lawyer's house to look for traces of the poison she finds only her body. Matthew, then, reveals to Archie the detail that exonerates him: he can show that in the Valerian drink he had only put a sleeping pill. Wolfe immediately understands who the culprit is, but he must be flushed out ...

In a fashion studio, a wearer eats a candy contained in a red box and dies poisoned. Nero Wolfe and Archie are called into question by Enrico Frost, cousin of one of the models investigated for murder (Elena). Wolfe quickly realizes that the main suspect is Elena who gave the tailor Lello De Angelis the box of candy, but did not take. While Elena's family proves to be very hostile to Wolfe, the girl reveals that in a month (when she reaches the age of majority) she will inherit a fortune ... She also tells him she is very attached to De Angelis: her family has known him since the war and then they lost sight of them for years and then found themselves in Rome.

While in class with two students - the Russian Ludlow and the American Faber - in the prestigious sports club in which she is a fencing instructor, Neya Tormic is accused by Mrs Falchi of the theft of a jewel. The cousin and colleague Carla asks for help from Nero Wolfe: Neya is none other than the daughter of the only woman whom the investigator has loved. Despite noticing that Carla also went to him to hide a microfilm, Wolfe is astonished and almost moved; that's why he sends Archie Goodwin to the club to investigate.

The clerk Otto Bertola hires Nero Wolfe to prove that the woman who has circuit and married the fragile son Lapo, the seductive Susanna, damaged his business together with Silk, just dismissed secretary. To investigate Archie Goodwin moved to the villa of Otto under cover as a new assistant; so he knows what Bertola calls "parasites": Lapo and Susanna, who seem to really love each other; his second wife, Trina, dedicated to alcohol and men; her brother, Ruggero, maintained with a passion for the game. And then Zanna, laido "family friend" who teases Otto, boasting of having blown him a contract. The death of the friend-rival, killed with a pistol shot, throws shadows on the fixer, who owned a recently stolen Beretta. But also other members of the family are equally suspect: Trina had been used by Zanna as a sex object for one night and Roger himself had money problems that he could lend to him. When even Silk, the former secretary, is found lifeless, killed by the same weapon of the first crime, Wolfe has further evidence against Otto, but he is not at all convinced that he is the culprit ...