A luxury sports car arrives packing heat, catching officers off-guard.

Customs and Border Protection forms one of the world's largest law enforcement agencies, drawing officers from many backgrounds. From rookies starting out, to veterans who have seen it all: at America's borders, the mission comes first for CBP officers.

Tourist Day attracts those who move south for the winter. Officers prepare for smugglers hiding inside crowds and parties fueled by alcohol and drugs.

Each year, CBP recovers over 1,300 stolen vehicles at ports of entry. Many are heading for the black market, while cartels use others for trafficking.

At critical junctions along the U.S./Mexico trade arteries, hidden goods worth billions of dollars cross the southern border. Drug seizures at that border are at an all-time high as the cartels attempt to smuggle both large and small loads of narcotics.

Cartels hope CBP won't inspect happy families, but officers know not to fall for that smuggling trick. Due to avian flu, live chickens can't be brought into the U.S. A family is forced to choose: go home to save their pet or surrender the bird to CBP.

Two men arrive in an SUV carrying enough suitcases for an entire family. Officers discover it's no family car -- it's a Kevlar-lined, bulletproof tank, the type that the cartels use to transport high-ranking gang members and attack law enforcement.

A traveler is caught with blades for cockfighting, a cartel-run blood sport; every year, Mexico grows millions of dollars of flowers for the U.S., but cartels are taking advantage of the influx of shipments during major holidays to stash something extra.

During his first day on the job, a rookie officer relies on his training, sending a hesitant driver for further inspection, and his hunch pays off; when a traveler claims to be visiting his dentist bimonthly in Mexico, officers investigate further.

Officers find that an 18-wheeler is carrying more than a load of takeout containers; a couple raises suspicion after declaring bulldog semen, but the labeling suggests the box may actually contain stallion semen, a valuable and tightly regulated substance.

With cartels using drones for surveillance and transport of narcotics and explosives, a newly formed CBP drone strike unit is taking aim at cartel eyes in the sky. An officer suspects that a vehicle may be carrying more than some innocent Santeria sprays.

A driver claims he buys used cars over the border to import into the U.S., but an X-ray reveals something suspicious in his spare tire; when a traveler returning from Mexico declares protein-rich snacks at Customs, a Fish and Wildlife expert is called in.

Officers process thousands of families crossing the border every day. Some carry memories, while others carry contraband. Because sometimes, families who travel together ... smuggle together.

While some officers wear a badge, others wear a leash. Over a thousand highly-trained K9s are on the scent, and if something's hidden, they'll find it -- because at the border, man's best friend is a smuggler's worst nightmare.

When hidden among shipments of narcotics and firearms worth billions, even the most innocent-looking contraband -- like a simple snack, or sweet treat -- can be more than what it seems.