The story takes place in a modern metropolis called "Haicheng". On the surface, it looks like any bustling city, but deep underground in the city hides a huge ecosystem called the "Quiet Zone" - an independent, self-sufficient biosphere with unique plants and animals, and its air is fatally toxic to humans on the surface. Thirty years ago, the builders of the Quiet Zone, a group of scientists and engineers, signed a pact of silence to guard it secretly and prevent it from being exploited or destroyed by the outside world. Today, the first generation of guardians is old, and a multinational biotechnology company is detecting the existence of the Quiet Zone through abnormal means and starting a secret exploration and seizure plan. The core rules of guardianship and sacrifice are: Guardians cannot use direct violence to expose the existence of the Quiet Zone. They must act within the rules, use the city itself as a maze and weapon, and use wisdom, misdirection and even self-sacrifice to expel threats.
