"The Forty Thieves" is a famous tale from the collection of stories known as One Thousand and One Nights. It follows the adventures of Ali Baba, a poor woodcutter who discovers the secret den of a group of forty thieves. The thieves hide their treasure in a cave that can only be opened by saying the magical phrase "Open Sesame." After learning their secret, Ali Baba uses the treasure to improve his life, but he faces challenges from the thieves and their cunning leader, Cassim. The story explores themes of greed, loyalty, and cleverness, ultimately highlighting the triumph of good over evil.