Ruthless criminal attorney Raymond Cortell (Sidney Blackmer) is not above bending and twisting the law to suit his purposes, making him a well-paid pariah amongst his peers. Practically the only person who believes that Cortell's tactics are ethical is his faithful assistant Mary (Judith Allen), the daughter of police-lieutenant Jim Kennedy (Purnell Pratt). Mary finally gets a wake-up call when a criminal whom she's helped to acquit shoots down her father during a robbery. She then switches her allegiance to young detective Dave Britten (Norman Foster), who's been waiting a long time to get the goods on the unscrupulous Cortell. Behind the Green Lights was Mascot Pictures' next-to-last feature production before the studio was reorganized as Republic.