It was especially quiet in the dark. The safe passage was shrouded in a layer of black fog. Even with the infrared vision from their helmets, the visibility couldn't exceed 10 meters. Inside the helmet, they could only hear their own breathing. The atmosphere was so heavy that it made people go crazy. The darkness was like a prison, you couldn't see what was outside the prison. All you knew was that no matter how far you walked, you still couldn't leave this prison.

If not for ...