To Matthieu is a story about two brothers, Matthieu and Eric, who work at the same factory as their father in Normandy.
When their father is dismissed for smoking on the factory floor, Matthieu is outraged and tries to have him reinstated, but his efforts are in vain.
Eric, who has just gotten married and has a child on the way, is hesitant to cause trouble, and their fellow workers also refuse to help.
Tragedy strikes when Matthieu's father dies in a road accident, leading Matthieu to believe it was suicide.
Determined to seek revenge, Matthieu devises a plan to seduce his boss's wife, Claire, in order to humiliate his boss.
Seducing Claire turns out to be easier than expected, but things take an unexpected turn when Matthieu and Claire fall in love.