Hu Shiyun, who traveled through time and space to the early 20th century, met Zhou Yun, who also traveled through time. After the fall of Shanghai, the two parted hurriedly. After Hu Shiyun arrived in Nanjing, he communicated with Zhou Yun through letters, expressing the hesitation and pain of being unable to do anything caused by his own time travel. The journey from Nanjing to Peking, from beginning to end, is narrated by these seven letters.