Original: Shade sets the main plot of the novel in motion when he impetuously defies that law, and inadvertently initiates a chain of events that leads to the destruction of his colony's home, forcing their premature migration, and his separation from them.
Simplified: Shade sets the main plot of the novel in motion when he breaks  that law, and starts a chain of events that leads to the destruction of his group's home, forcing their premature migration, and his separation from them.