Its title notwithstanding, Le Rouge est Mis (The Red Light is On) is not a drama about prostitution. Instead, the story concentrates on the humdrum, workaday world of the professional criminal. Jean Gabin plays garage-owner Louis, whose establishment is a front for a robbery gang. Louis and his confederates are careful to keep up a normal, bourgeois veneer by day, indulging in crooked activities only when "the red light is on" at night. This status quo is upset when one of the gang members becomes convinced that Louis' younger brother is a squealer. Le Rouge est Mis was adapted from a novel by Auguste Le Breton, of Rififi fame.
~ Hal Erickson, All Movie Guide