Madame Loisel desperately wanted a fancy and better social life and she thinks that she is poor, and she's not satisfied with her life.
Monsieur Loisel goes through a lot of work to get Madame Loisel an invitation to a fancy party but she has nothing to wear and she doesn't want to go looking like a peasant.
Madame Loisel gets a new gown and she borrows a diamond necklace from a friend but once they get home she noticed that she had lost the necklace.
Mr. and Mrs. Loisel lied to Madame Forestier because they needed more time to either find the necklace or get a new one. They ended up using all of his father's inheritance, and a bunch of loans for a new one.
Madame Loisel gives the new necklace to Madame Forestier and then spends the next 10 years of her life living in an attic and paying off debt.
Madame Loisel sees Madame Forestier 10 years later and tells her that she's the reason she looks like death because she lost the necklace. Madame Forester ends up telling her that the original necklace was fake
Oh really? Mine was a fake
I worked my butt off to pay for your necklace cause i lost it!