Mr. Topaze is an unassuming school teacher in an unassuming small French town, who is honest to a fault. He is fired when he refuses to give a passing grade to a bad student, the grandson of a wealthy baroness. Castel Benac, a government official who runs a crooked financial business on the side, is persuaded by his mistress, Suzy, a musical comedy actress, to hire Mr. Topaze as the front man for his business. Gradually, Topaze becomes a rapacious financier who sacrifices his honesty for success...
