"The Valachi Papers" by Peter Maas, provides an account of the internal workings of the Cosa Nostra, the Italian arm of the criminal underworld in the United States, as provided by one of its members. Joseph Valachi is a soldier in the Cosa Nostra for thirty years. He largely escapes jail time, but during the latter part of his "career," he receives a twenty year sentence on a narcotics charge. Valachi has just begun his sentence when he is whisked away to New York by Federal agents. The agents hope to pressure Valachi into talking about his drug operation by threatening him with another narcotics charge. Valachi refuses to talk and is returned to the Federal prison in Atlanta. Crime boss Vito Genovese is serving time at the same facility. He becomes suspicious that Valachi may have talked and puts a mark out on Valachi. Under the overwhelming pressure of having his life at risk, Valachi mistakes a fellow inmate for a potential assassin and kills him. Valachi is arrested for murder one but the charge is reduced to second degree murder when Valachi agrees to finally talk.

The timing for Valachi's revelations is ideal. Prior to the installation of Attorney General Robert Kennedy, the FBI's main focus had been hunting down domestic communists, neglecting the crime underworld at large. However, Kennedy gives the Justice Department new direction and focus is shifted to organized crime. In an effort to play catch-up in their knowledge about the underworld, the FBI frantically collects massive amounts of intelligence via electronic bugs and wiretaps.

At the time of Valachi's revelations, the FBI has strong suspicions that an organized crime syndicate exists but evidence is scarce and not conclusive. The account and details provided by Valachi, who the authorities feel has perfect retention, astounds the authorities. Through their recent electronic surveillance, the phrase "Cosa Nostra" has popped up occasionally but its meaning or importance is unknown. When an agent asks, early during his interviews, if the organization is the Mafia, Valachi corrects the agent. The Mafia is what outsiders call the Italian crime syndicate—insiders call it Cosa Nostra. Literally translated, Cosa Nostra translates to "our thing."

Valachi provides the FBI with the organizational structure of the Cosa Nostra. Cities, or in the case of New York City, portions of cities, are controlled by Families. Within each family is a Boss, Underboss, lieutenant and soldiers. While there are very few requirements to be a member of the Cosa Nostra, those requirements are intractable: all members have to be Italian, loyal to their Family and take a vow to never reveal the existence of the organization. Valachi confirms the hundreds of murders and other activities of the Cosa Nostra Families of New York City. The information obtained from Valachi is confirmed against the information they already have and the Federal authorities feel confident that it is reliable and invaluable.

For his safety, Valachi winds up serving his sentence in solitary confinement—a mark is on his head for violating the vow of loyalty and silence as a member of the Cosa Nostra. Although the Cosa Nostra continues to operate after Valachi's revelations, they will never be as powerful as they once were. The Cosa Nostra is successful in part due to their elusive mystique and ability to operate in the shadows. With his astonishing revelations, Valachi shatters that advantage forever.