Michel Piccoli is irresistibly slimy in the role of a conniving attorney. Making the acquaintance of two lovely sisters (Romy Schneider and Andrea Ferreol), Piccoli seduces them both. He then invites the sisters into his latest scam: marrying and murdering gullible men and women, then cheating their insurance companies. The noirish intrigues of Infernal Trio are all the more remarkable in that they are based on a true story. It shouldn't be too surprising to first-year French students that the original title of this French/Italian melodrama was Le Trio Infernal.
~ Hal Erickson, All Movie Guide