2. Fentanyl

Mariana investigates fentanyl, a contributor to the deadliest drug crisis in U.S. history.

3. Counterfeiting

Mariana meets the craftsmen who make and sell the world's finest counterfeit U.S. dollars.

4. Steroids

Mariana attempts to understand the vanity, insecurity and greed that drives steroid use.

5. Pimps

Mariana sets out to understand the ugly business of illicit sex in America.

6. Cocaine

Mariana retraces one of the world's most intractable smuggling routes, following cocaine's path around the world - from the Peruvian jungles, to the Colombian coastline, and to the streets of Miami.

7. Tigers

Mariana van Zeller tackles the black market for tigers and tiger parts, so secretive and dangerous that few have attempted to uncover its ugly details.

8. Guns

Mariana uncovers a supply chain of firearms being smuggled into the hands of drug cartels.