Cracks in Time and Space

Bizarre "cracks" appear in different time and space stitched wirelessly. People in a certain time and space in the universe specialize in maintaining and repairing cracks in time and space. Yet even they don't know "who" they are and why they do what they do. There are cracks in time and space, which will cause people from different eras and different ancient nationalities to appear in "outside places". A person codenamed Bing Guhan and her friend Fu Qihao and others want to send back the human beings who are strangers in a foreign land, and also repair the cracks.