After Nero Wolfe reacts petulantly to a change in one of his favorite meals, his assistant Archie Goodwin decides to prank him by inviting a neighborhood boy, Pete Drossos, into the house to consult with Wolfe on what Pete believes is a case. Pete claims that a woman wearing distinctive golden spider-shaped earrings asked him to fetch a police officer while he was cleaning the windshield of the car she was driving at a stoplight, and he believes that her male passenger was holding her hostage.
The next night, the pair are shocked when NYPD Sgt. Purley Stebbins informs them that Pete has been killed by a hit-and-run driver, as well as INS agent Matthew Birch. Soon after, Pete's mother brings Wolfe $4.30 that Pete has saved and asks him to find Pete's killer.
Angered by Wolfe's reluctance to get involved, Archie uses the money to place an advert in the newspapers asking for the woman driving the car to contact Wolfe. Wealthy widow Laura Fromm arrives at Wolfe's office wearing the golden spider earrings and asking to hire his services. Wolfe suspects that Fromm knows who the driver is, but she refuses to reveal it; the next day, Fromm is also murdered in an apparent hit-and-run. Angered that two people who came to him for help are now dead, Wolfe decides to solve the murders.
Wolfe identifies a charitable organization that Mrs Fromm supported as a likely link between the deaths. Archie begins to investigate various individuals connected to the charity: Fromm's secretary, Jean Estey, director Angela Wright, public relations manager Paul Kuffner, and the wife of the charity's attorney, Dennis Horan. It is revealed that the charity is part of a blackmail ring targeting desperate refugees who are in America illegally. Horan attempts to distance himself from the other men, but when they learn this, the others identify him as a key ringleader of the blackmail scheme, along with Birch. Birch, however, took orders from an unknown woman.
Gathering the principal suspects in his office, Wolfe reveals the identity of the murderer — Jean Estey. Estey was a key figure with the blackmail ring, but Fromm had overheard the code words she used with her confederates — "said the spider to the fly" — and had begun to suspect her, giving her the earrings to try and provoke a response.
> said the spider to the fly
It is implied that Birch captured Estey to 'handle her' because she was taking too large of a share of the profits, prompting her to panic and try to contact Pete for help. After killing Birch, Estey realized that Pete could identify her and so killed him, too. Her third homicide was of Mrs. Fromm after the dinner at Horan's, feeling pressured after she had cut a $10,000 check to Nero Wolfe to investigate.
Estey is identified by the tailor who sold her the men's clothing she used as a disguise and is arrested. The case ends with Archie giving half the fee Wolfe has earned to Pete's mother.
