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 ...