Rachel Bruner, a wealthy Manhattan widow, has recently incurred the wrath of the Federal Bureau of Investigation. After reading The FBI Nobody Knows , a prominent critique of the many unethical practices of the Bureau, she has mailed 10,000 copies of it to prominent figures across the country. Having endured several incidents of harassment and prying, she offers to hire Wolfe to persuade the FBI to leave her alone. Although initially hesitant of making a powerful enemy, Wolfe is persuaded over Archie’s objections when Bruner offers a $50,000 retainer and then doubles it, on top of any expenses he may incur. He is also sympathetic to both Bruner’s plight and the arguments made in the book, and decides not to withdraw in the face of what he sees as heavy-handed opposition tactics.
As the FBI put Wolfe and Archie under surveillance, Wolfe plans to gain examples of FBI malfeasance and use it to persuade the FBI to back down. Archie’s initial investigations prove fruitless, but he soon receives an anonymous message from Dr. Vollmer, Wolfe’s physician, asking for a clandestine meeting. Although initially suspecting an FBI trap, Archie is astonished to learn that the message is from Inspector Cramer. Cramer reveals that theFBI are attempting to have Wolfe and Archie’s private investigator licenses revoked. He also reveals that he suspects that FBI agents may be involved in the murder of Morris Althaus, a freelance journalist who was researching an article critical of the Bureau, two months earlier. Althaus was foundshot to death in his apartment, but the fatal bullet was never recovered; in addition, his research notes were also missing. Cramer, who is opposed to the FBI’s efforts to sabotage Wolfe and stonewall the police's homicide investigation, offers to write a report favourable to Wolfe and Archie ifWolfe proves that the FBI are responsible for the murder of Althaus.
Wolfe instead decides that it would serve his purposes better to prove that the FBI had no part in the murder. He also devises a plan to trap the FBI. Acting on the suspicion that the FBI have secretly bugged Wolfe’s office, Wolfe gathers the key suspects in his office and publicly claims that he is gathering proof that FBI agents murdered Althaus and are covering it up, while directing Archie to conduct his own investigation.
Archie discovers that Sarah Dacos, Bruner’s secretary, lives in the same apartment building as Althaus and claimed to have seen FBI agents leaving the apartment on the night of the murder. When Wolfe and Archie question her, Dacos claims only a casual acquaintance with Althaus, but Archie remains suspicious of her. Acting on a hunch, hebreaks into Dacos’s apartment, where he discovers proof that Dacos and Althaus were having an affair. He also discovers the gun that was used to kill Althaus. Archie realises that Dacos murdered Althaus after he broke off their relationship to marry another woman, and that he needs to leave the gun behind. He moves it to a new hiding place, but worries that Dacos will dispose of it before Wolfe and Archie can prove her guilt.
Meanwhile, Wolfe has been preparing his trap for the FBI. Publicly arranging a dinner with his old friend and fellow orchid lover Lewis Hewitt, he privately hires two actors resembling himself and Archie and has them smuggled into the brownstone, along with his operatives Saul Panzer, Fred Durkin and Orrie Cather. The actors are sent to Hewitt’s dinner posing as Wolfe and Archie, while Wolfe, Archie and the operatives secretly remain in the brownstone. Having spread his public suspicions of the FBI and his plans for the house to be empty, Wolfe suspects that the FBI will use the opportunity to break in and steal any evidence he has that FBI agents murdered Althaus.
Two agents break into the house that night, only to be held at gunpoint by Archie and the operatives. Wolfe confiscates their credentials, having obtained conclusive proof of the FBI's harassment of a private citizen. The next day, Wolfe meets with senior FBI official Richard Wragg and offers a deal, with Bruner watching through the office peephole. Wolfe refuses to return the credentials, but offers to abstain from pressing charges and publicly embarrassing the FBI, in exchange for the FBI ceasing all surveillance and harassment of Bruner and those connected to her, including Archie and himself. He adds that he can prove that FBI agents were not responsible for Althaus' murder.
After Wragg agrees to Wolfe’s terms, Archie approaches Inspector Cramer and gives him a lead on Dacos. After the police search her apartment and find the gun, Dacos is arrested for the murder. Wolfe then gathers Wragg and Cramer in his office and negotiates a deal between them. In exchange for Wragg handing over the missingbullet that will prove Dacos' guilt, taken by the FBI along with Althaus' research notes, Cramer will conceal any involvement on the part of the FBI. Wragg and Cramer reluctantly agree to Wolfe’s deal.
The novel ends with Wolfe and Archie receiving an unidentified but important visitor, implied to be J. Edgar Hoover. Speculating that he has come in person to collect the FBI credentials, Wolfe refuses to let him into the house, leaving the visitor to keep ringing the doorbell.