Mr. Topaze (Peter Sellers) 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 (Herbert Lom), a government official who runs a crooked financial business on the side, is persuaded by his mistress, Suzy (Nadia Gray), 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 and, in a final stroke of business bravado, fires Benac and acquires Suzy in the deal. An old friend and colleague, Tamise (Michael Gough) questions him and tells Topaze that what he now says and practices indicates there are no more honest men.

A vicious gang of crooks plan to steal the wages of a local factory, but their carefully laid plans go wrong, when the factory employs an armoured van to carry the cash. The gang still go ahead with the robbery, but when the driver of the armoured van is killed in the raid, his wife plans revenge, and with the police closing in, the gang start to turn on each other.

A gang of criminals plan to use a marriage agency that they won during a card game, to arrange a lucrative marriage for one of their number.

Back in London after serving time, an ex-convict learns that his wife is not willing to return to him. He plans to crack a safe at a club.