Guy de Maupassant's "The Necklace" is a story about a woman (Madame Loisel) who desires nothing more than to be wealthy and accepted by the elite. In order to fit in, Madame Loisel borrows a necklace from Madame Forestier. Unfortunately for Madame Loisel, the necklace goes missing. She and her husband spend the next ten years paying off the loans they took out to replace the necklace. In the end, readers learn that the necklace was paste (fake). Madame Loisel and her husband ended up in extreme poverty for nothing.
As for why it takes Madame Forestier a little while to recognize her old friend, Madame Loisel has changed. Her life over the past tens years has been a hard one. She no longer looks like the young and beautiful woman she once was. Instead, Madame Forestier believes her to be a "plain good-wife."