For many years, the FBI, led by J. Edgar Hoover, ignored organized crime, as the Bureau regarded local law enforcement as best equipped to handle it. That changed when Attorney General Robert F. Kennedy (in the 1960s) and New York City's Rudy Giuliani (in the 1980s) pursued eradication of the Mafia..

In this book, readers are introduced to several characters in the American Mafia, known as "rats" in the criminal world, whose cooperation with law enforcement resulted in the arrest of Mafia members across the country. Short biographies of each informant detail their crimes and deals made to stay alive or reduce lengthy prison sentences. FBI and CIA records released in 2017, and books written by the criminals themselves, reveal why previously loyal Mafia members and associates became informants. Most of the criminals written about are dead; a few are presumed to be alive and in the witness protection program.