Answer:
The couple was aghast because the necklace they had borrowed was lost. As a consequence they might face a lot of problems if they couldn't find the missing necklace. They had to buy the necklace and return it.
Step-by-step explanation:
The climax of the story "The Necklace" arrives when the couple lost the necklace. Madame Loisel and Monsieur Loisel was very depressed and felt aghast when they realized that the necklace was lost. The necklace belonged to Madame Forestier. They found everywhere but were unable to find the necklace. As a consequence of the lost necklace, the couple had to buy the same and return. They planned to replace the necklace by purchasing the same from the jeweler shop. They started to borrow money and work hard in order to pay for it. It took a total of ten years for them to pay the debts of the lost necklace.