"We will focus on a certain character in one or two successive episodes to thread all the clues about him or her, so that our audience can understand clearly what happens to different characters."

Compared with image, sound can give listeners bigger scope for imagination, "which means a radio play might be one of the best forms to present science fiction", Liu says in the trailer of the radio play.

Apart from script writing, another difficulty in making this radio play was to find the right voice performers. There are more than 40 voice actors and actresses in the first season.

"When interviewing performers, we need to see whether their voices can match the image of the roles and whether they can properly represent the characters," says Liu Cong, director of the play, and also the performer of Da Shi, the policeman.

The most difficult thing is how to use voice to show people's spiritual state in a different time, like during the "cultural revolution" (1966-76), he says.