Undercover ATF and DEA Agents are reminded to never judge a book by its cover and to always be on their toes. Even small-time suspects have the potential to unleash terror—and no place seems safe.

ATF Undercover agent Dominick Polifrone aims to pass himself off as a mobster to stop the Iceman serial killer. Bergen County Undercover Detective Carlos James poses as a gang member to disrupt a treacherous plot against a woman's ex.

ATF Special Agent Perala is reminded of the importance of listening to your gut; in New York, a tipster claims that a man awaiting trial is planning an attack on his alleged rape victim before she can testify; and more.

ATF Special Agents Dobyns and Kilday put their best feet forward only to have their lives put on the line. Once the investigation wraps, will they become targets for revenge?

An Undercover NYPD officer and an ATF Special Agent learn firsthand not to trust a suspect's demeanor, regardless of how amicable it may appear.

Undercover agents Lyle Kirian and Brian Townsend embed themselves in two different, but equally dangerous worlds in order to investigate suspected local gang members, and the Mexican Cartel.

One FBI undercover agent meets with suspects in Denmark in an effort to retrieve one of the world's lost treasures, while another agent takes on an unlikely suspect believed to be planning a murder for hire.

NYPD Officer turned undercover agent Jerry Speziale finds that a bullet changes the trajectory of his career. Fish and Wildlife Service's Special Agent Ed Newcomer investigates the senseless hawk killings in California.

ATF Agent Scott Perala takes down a career criminal, FBI Agent Robert Wittman investigates a man pretending to be a sheik selling fake artwork, and Broward County Detective Cesar Morales stops a string of robberies.

On his last day as an undercover agent, Bergen County Detective Carlos James experiences his first shootout. ATF Agent Jenn Eskew poses as a hitwoman. An undercover operation with unveils who may be pulling the strings in Charlotte's government.

The real stories of dangerous undercover police work through video and audio recordings of the officers in the moment as well as interviews with the people closest to the action.