Madame is in the middle class with dreams of moving to the upper class, but she has little hope because she married a guy in the middle class.
She is invited to an upper-class party, but she doesn't have a dress or jewelry.
Madame is worried that she would look poor among all the rich people if she did not have nice clothes or jewelry.
Madame received a necklace from her rich friend, and went to the ball. She was the talk of the town because she was so pretty. Near the end of the party she left in a rush afraid they would find out who she really is.
Madame lost the diamond necklace that her friend gave her.
After 10 years of debt, Madame finally payed off the diamond necklace. She ran into her friend and confessed that she lost her necklace and it took her 10 years to pay off. Her friend told her what a horrible mistake she made because original necklace was made out of paste, and not diamond.