Comedy centering on Éraste, who is in love with Isabelle. Mme. Argante, Isabelle's mother, promises Éraste her daughter's hand if he inherits the major portion of his uncle Géronte's fortune. Although an invalid, the old man takes a fancy to Isabelle and plans to marry her himself, but he is dissuaded. He finally decides to make Éraste his heir but also plans to make bequests to a rural nephew and niece.
Masquerading as each of these two characters, Érasté's rascally valet Crispin makes them appear so disagreeable that Géronte changes his mind about their bequests. Soon afterward he falls into a coma and, to the horror of his heir presumptive, seems about to die intestate.
Crispin disguises himself as the elderly invalid, calls the notaries, and makes a will, also providing generous annuities for himself and Géronte's servant Lisette, whom he loves. When Géronte recovers from his coma, the worried conspirators finally manage to convince him that he himself dictated the will. He is persuaded to let it stand. Thus Éraste marries Isabelle, and Crispin marries Lisette.