It tells the story of a modest school teacher who is fired for being too honest and decides to become a dishonest businessman.
Ernestine, the daughter of the school principal Mr. Muche, takes advantage of him, making him do her paperwork and watch her students, but Topaze naively takes this to be a mark of affection and asks his friend Tamise, another teacher, to quietly see if Mr. Muche would let Ernestine marry.
In the meantime, a young woman named Suzy Courtois arrives; she is the aunt of a private student of Topaze and intends to enroll the child at the school, but she changes her mind after visiting.
Topaze is now the director of a business firm, but his "good luck" doesn't make him happy; he is tormented by his conscience and constantly fears arrest, and he has discovered that Suzy is Castel-Benac's accomplice and mistress as opposed to victim.
He spurns Ernestine and Mr. Muche in favor of Suzy, and continues to work as Castel-Benac's frontman despite knowing the truth.