Here's how it plays out:
* The warden's secret: The warden of Camp Green Lake is a greedy woman who has been using the camp as a way to steal valuable items from people who were sent there. She uses the boys to dig holes as a cover, but she's really searching for a treasure that was buried long ago.
* The mail connection: The warden's plan involves a connection to the mail. She steals letters from people, searching for clues about the treasure. These letters are then buried in the holes the boys dig.
* Stanley's role: Stanley Yelnats, the main character, is sent to Camp Green Lake because of a misunderstanding about a pair of sneakers. The sneakers happen to be the same pair that the warden stole from a man whose letters she was also searching for. Stanley's connection to the sneakers makes him a target for the warden, and she tries to use him to help find the treasure.
* The mystery unfolds: Stanley's journey to discover the truth about the mail problem and the warden's motives leads him to uncover a hidden history of the area and a series of interconnected events involving stolen treasure, lost love, and the importance of kindness.
The mail problem is a key element in the plot of Holes. It serves as a driving force behind Stanley's journey, highlighting the warden's greed, the injustice of the camp, and the interconnectedness of seemingly unrelated events.