Final answer:
The crisis in "The Necklace" occurs when Mathilde discovers the necklace she borrowed and lost is valuable, leading to years of poverty to replace it, only to learn it was costume jewelry.
Step-by-step explanation:
The crisis of "The Necklace" occurs when the main character, Mathilde Loisel, realizes that the necklace she borrowed from her friend and has lost is actually a high-value item. The crisis point in a literary work is often the climax or turning point, where the main characters' fortunes take a definitive turn, usually for the worse in the case of a tragedy. In "The Necklace" by Guy de Maupassant, this moment is characterized by a frantic turn of events that lead to Mathilde and her husband living many years in poverty in order to replace the lost necklace, only to discover that the original was not made of real diamonds but was instead costume jewelry.