What is the main conflict in The Doorbell Rang by Rex Stout?

In The Doorbell Rang, eccentric New York detective Nero Wolfe goes up against J. Edgar Hoover's FBI. Mrs. Rachel Bruner has sent a book critical of the FBI to 10,000 important people, and now she's under investigation and wants it to stop. With the lure of a $100,000 retainer, Wolfe sets out to find dirt on the FBI. Instead, he uncovers the murder of Morris Althaus, not by three FBI agents on the scene, but by Althaus's rejected lover. Wolfe tricks the FBI into invading his home, and under threat of disclosure of their illegal acts, he forces the FBI to stop investigating his client.