Domino (1976)

Lorette is married to Heller, a very jealous husband who has discovered a love letter from a former lover named François. He suspects (rightly so) Crémone, his best friend, and has vowed to destroy this rival. Lorette recruits a man, François Dominique, known as "Domino," to divert Heller's suspicions away from her former lover... who did indeed write the infamous letter. Domino will temporarily divert Heller's suspicions but will ultimately give rise to far more serious ones...