Of all the tools available to law enforcement, the living, breathing undercover operative remains the gold standard. This is true in TV shows and in the real world. In the era of electronic surveillance, UC work enforces accountability; it prevents mistakes, and of all the boots on the ground, undercover agents are often the most valuable.

The FBI generally has about 100 UC agents working full-time in the field. In the 1990s and 2000s, Marc Ruskin had the most diverse, and notorious, case list of all, and the broadest experience within the bureaucracy, including overseas. He worked ops targeting public corruption, corporate fraud, Wall Street scams, narcotics trafficking, La Cosa Nostra, counterfeiting-and gritty street-level scams and schemes.

Sometimes working three or four cases simultaneously, Ruskin switched identities by the day: Each morning he had to walk out the door with the correct ID, clothes, accessories and frame of mind for that day's mission. Meet Alex Perez, Alejandro Marconi, and Sal Morelli, just a few of Ruskin's undercover personas.

And how is the right UC agent chosen, how is a bogus identity manufactured and "backstopped," how is the Bureau's long-term con painstakingly assembled? No one has ever given us the inside story like Ruskin. The Pretender is the definitive narrative of undercover ops-the procedures, the successes, the failures--and the changes in the culture of the new-era FBI.