Final answer:
The story is about attackers who attempt to kill Santiago but instead face mystical consequences, with their target Gil-Dong sparing them under a strict condition.
Step-by-step explanation:
The story told by one of the attackers in the pyramids involves a tense and mystical encounter. After the assassins fail to kill the boy, Santiago, they end up turning on each other and killing their guide. Surrounded by mountains and in the midst of a fierce storm, they are confronted by the boy they were trying to kill, who is now empowered and riding a donkey while playing a flute. The boy, revealing himself as Gil-Dong, disarms the attackers and spares their lives on the condition that they promise never to attempt to take a life again, warning them that he would know and would not hesitate to kill them if they broke their promise.