American agent Murphy and Mexican agent Montalban join forces and go undercover, infiltrating a ring that is smuggling Mexicans into California to work the fields of crooked rancher da Silva. Murphy pretends to be a small-time hood joining da Silva's gang while Montalban gets himself
smuggled in as one of the workers. Murphy is found out, and in a horrifying, effective scene is run over by a tractor while Montalban watches helplessly. But Montalban gets even in the climactic shootout in a quicksand-filled swamp. Mann's use of the southwestern landscape foreshadows the westerns
he began to make the following year.