Based on the novel by Hannelore Cayre, the story centers around Patience Portefeux (Isabelle Huppert), an underpaid, overworked French-Arabic translator in charge of phone surveillance for a narcotics police unit. When she realizes she knows the mother of one of the drug dealers, Patience decides to cover for him and gets herself more and more deeply involved in the world of drug trafficking. Soon, she is using her insider knowledge and police resources to build her own crime network and earns the name "Mama Weed".