Her name is Mathilde Loisel. "She was one of those pretty, charming young women who are born, as if an error of fate, into a petty official's family." (pg. 373) She slipped into a marriage with a simple civil servant. She suffered constantly wanting to feel the luxury of a rich woman.
Mr. Loisel comes home with an invitation to a Ball. At first she is upset as she has nothing to wear but he offers to buy her a dress for the occasion. "I'll give you four hundred francs. But try to get something really nice." (pg. 375) They agree to go to the ball.
She felt she needed some jewerly. Her husband suggested: "Why don't you go and see Madame Forestier and ask her to lend you some jewelry." (pg. 376) So she goes to her friend and asks to borrow a diamond necklace.
Mrs. Loisel went to the ball and had the best time of her life. The fun ended when she got home."The...the...necklace---it's gone." (pg. 377) She tells her friend that she broke the clasp and was getting fixed while they looked for it
They accept that they are not going to find it and they borrowed money to get one just like it. They had a lot of debt and they worked to pay it off. "And it went on like that for ten years" (pg. 379) They worked for ten years to pay off the debt off the necklace.
After everything and paying off her debt she sees her friend and decides to tell her everything. Her friend then admits:"Oh, my poor, poor Mathilde! mine was false. It was worth five hundred francs at the most!" (ch. 380) So there was no need for her to work all that time at all. It was all for nothing.