It's the final leg of their perilous journey and the six must face sweltering heat during the day and nights that drop below zero – how long can they last?

Things get real in gang controlled Arriaga, when the six climb atop a cargo train known as "La Bestia," or "The Beast."

The six are split into three groups, each tasked with retracing one dead migrant's past, and discover the grave circumstances that led "their" migrants to risk their lives.

Six Americans – strangers from all walks of life – gather to embark on a haunting journey that begins in the Pima County morgue's dead-body freezer.