Director Liu Cong.[Photo provided to China Daily]

One of the key principles for radio play adaptation is to fully respect the original work and change or delete as little as possible. "It's because most of the audience are fans of the books or those who decide to listen due to the books' fame, so they want the authentic story," Cheng says. However, she deletes visual descriptions, such as those about views and clothing, if it does not influence the plot.

To attract the attention of listeners, within each episode, scriptwriters need to create a kind of psychological rhythm by setting up small conflicts, big conflicts and the climax, she says.

There are other difficulties. One is how to use sound to represent spectacular scenes. Another is how to explain, in a simple but interesting way, the complex scientific concepts that stretch over pages in the novel.

"Because listeners can only concentrate for a limited time, it's no good to explain the concepts through monologues or dialogues. Instead we usually use sound effects to achieve that purpose," Cheng says.

"Luckily, Liu uses a lot of metaphors to explain those concepts, which I will keep."

Although the radio play adaptation needs to be authentic, compared with the first book, the second book of the trilogy, Dark Forest, contains too many characters and a complicated narrative, in which Liu hides the clues.

"It's impossible to do the play according to the plot of the novel. So I created an Excel sheet to map out all the characters, all the page numbers and paragraphs about them, as well as the content," Cheng says.