When his wife and her lover are found dead, real estate broker Julien Vercel (Jean-Louis Trintignant) becomes the prime suspect in the murders. To save himself from a long prison sentence, Julien turns to his trusty secretary, Barbara (Fanny Ardant), to investigate. Barbara, who has been secretly in love with her boss for some time, dedicates herself to her new responsibilities as a private detective -- and quickly manages to dig up some shocking information about Vercel's wife.