Season 4

Agents put themselves in harm’s way searching for armed smugglers fleeing a shoot-out with the Mexican military. Once at the riverbanks, they find a suspected smuggler who has been shot five times. Their mission quickly changes as they rush to save the man’s life.

Drug smuggling has reached “Texas-sized” proportions in the Rio Grande Valley. A canine unit detects a suspicious vehicle coming in from Mexico, and agents discover a massive quantity of methamphetamine concealed within.

Law enforcement battles to intercept the massive flow of illicit traffic moving through the Rio Grande Valley. Agents in McAllen, Texas, track a group of illegal immigrants in the dark and find themselves outnumbered in a large field.

The Rio Grande River serves as a highway for illegal traffic and dangerous crossings. As the Department of Homeland Security’s surveillance intensifies, powerful drug cartels and human smugglers are trying more desperate tactics.

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.

A Blackhawk helicopter leads ground agents on an epic chase after an illegal immigrant through treacherous mountains near Douglas, Ariz. A live surveillance camera alerts Border Patrol agents to a known fence coyote who tries to guide illegal immigrants into downtown Nogales.

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. Agents arrest the driver and seize the drugs, then pursue the smugglers.

Downtown, Border Patrol and ICE agents discover a major drug-running tunnel and suspected smugglers may still be inside. With cartels watching their every move, they must risk their lives to map and destroy it.

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.

Illegal traffic between the Rio Grande and the Falfurrias Checkpoint in South Texas.

Tactical cat-and-mouse games used in the war on drugs.