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 ...