Border Wars - Season 4 (2012)

The Border Patrol fights back against the criminals who use the Rio Grande to cross the border with their contraband.

In the southern border towns of Douglas and Nogales, Ariz., agents uncover new and more cunning methods smugglers create to avoid detection, including a drug tunnel under the border.

Along the southern Arizona border at the port of entry, agents detain two families within a 24-hour period, driving similar SUVs and carrying a combined total of nearly $1 million in cash and drugs.

Agents and officers work around the clock to secure the border between El Paso, Texas, and Ciudad Juarez, Mexico.

Border Patrol agents cut off a getaway car as it tries to flee the scene of a drug drop in ranchland east of Nogales, Ariz.

Downtown, Border Patrol and ICE agents discover a major drug-running tunnel and suspected smugglers may still be inside.

In Puerto Rico, agents keep a high-value drug seizure from South America secure as they transport it back to San Juan. They also use a DASH 8 plane and radar to find and seize a small drug-running boat in the dangerous Mona Passage.

Agents in Puerto Rico enter one of San Juan's most notorious housing projects for an undercover "buy and bust" operation to intercept a dump truck full of cocaine, and race to find illegal immigrants who have landed on a secluded beach.

When the Coast Guard rescues Cuban refugees from a remote island in the Mona Passage, Customs and Border Protection agents must race to intercept them and verify their identities.