On a Sunday morning outside the church of a provincial town those who do not attend mass are strolling around. Among the bowlers is Landry, a young clerk who is a witty merrymaker. He invites the strollers to drink a toast to his boss Maître André, a graybeard married to Jacqueline, a lovely and honorable woman.
Maître Subtil and his nephew Fortunio arrive from the country. The old uncle wants the young man to work in Maître André’s office and leaves him in his cousin Landry’s care. Fortunio dreams of love and is afraid of life but Landry intends to teach him how to take advantage of both.
Among the soldiers wandering in the square, captain Clavaroche, a newcomer and a lady-killer, enquires about women to seduce. He sets his heart on Jacqueline, whose virtue is matched by her beauty, and who is just coming from mass. Under the pretext of resistance, Jacqueline owns a dull marital life before introducing her husband to the womanizer. Using flattery, the captain gains the notary’s favor and is invited for dinner. Dazzled by Jacqueline, Fortunio decides to become a clerk.
A few days later in the early hours, Maître André has difficulties waking up his wife and more so getting explanations about the man who came into her bedroom by night according to his clerk Guillaume. On their wedding anniversary, Jacqueline heaps reproaches on him, feigns despair and fools him into believing he should not be jealous.
No sooner has the husband gone than Clavaroche steps out of the closet. How could they defend their romance? Clavaroche suggests to Jacqueline that she should find a decoy, namely to let a young man court her in return for some flirtation so that André’s suspicion is diverted on to the innocent man.
Among the clerks who come to compliment Jacqueline, her maid advises her to choose blushing Fortunio. In private, he unveils his shyness and spiritedly promises Jacqueline unlimited devotion, especially when he understands that she needs him.
While the clerks are discussing Jacqueline’s alleged infidelities, Clavaroche can speak to her before Maître André arrives for dinner.
The husband introduces Jacqueline to Fortunio, whom he has accepted to escort his wife so as to show he is not jealous. Everything is fine except that Jacqueline is dreamy and while toasting, Fortunio’s song sows confusion in her mind.
While husband and lover are playing cards, the woman tenderly questions her young sweetheart and welcomes his passion.
Clavaroche tells Jacqueline that the notary, whose jealousy is rekindled by a new account from Guillaume, will station armed men that evening under her window. Luckily, he will be among them and plans to trap Fortunio through a false date. But the latter overheard everything.
Jacqueline wants to save Fortunio as he tells her that he will throw himself into the ambush from despair of being manipulated. In the face of his determination, she admits that only him inspired her with true love, then she must conceal him hastily.
The sun rises and Maître André, followed by suspicious Clavaroche, comes in to offer his apologies. He discharges the watch and dismisses Guillaume for slander. Holding a candlestick to light their way, the husband and the lover bid good night to Jacqueline and leave her alone… with Fortunio!