Mathilde married a clerk. They have a maid, but she feels like her life isn't good enough. She wants more in life.
Her and her husband got invited to a ball, but she doesn't have a dress to wear or even decorations. Her husband gives her 40,000 frances for a dress. He then suggests that she borrows a necklace from her friend.
They go to the dance and she was the "life of the party." Everyone wanted to be introduced to her.
They took a carriage home. Once they got home they realize the necklace is missing. Her husband goes out and looks for it but comes back with nothing. They write her friend and tell her the clasp broke and it's being repaired.
They bought a replacement diamond necklace and went to every "loan shark" they could find. In doing so they became poor, having to pay all of them off for 10 years.
One day Mathilde runs into her friend, Margret and tells her all about the replacement and loans. Her friend then proceeds to tell her that the necklace was plaster. It wasn't real diamond.