The plot of the science fiction series "San Ti" is based on a story from the literary trilogy "Memory of the Earth's Past" by the science fiction writer Liu Cixin. The events take place in China during the "Cultural Revolution". Astrophysicist Ye Wenjie, who is leading the top-secret project "Red Coast", writes a letter to extraterrestrials inviting them to visit planet Earth... Some time later, representatives of the special services encounter an inexplicable phenomenon.