Cuatro en la frontera

Also known as De l'or dans la vallée, Quattro alla frontiera

A French National Treasury van is assaulted and they steal the gold bullion it was carrying. According to confidences received by the Police Headquarters of Barcelona, it seems that part of the gold is clandestinely introduced into Spain through the Pyrenees. In order to discover and eradicate such smuggling infiltration, an agent pretends to be a day laborer at a farm located on the border and in a suspicious area.