Chen Huaian found an old unsent letter among his grandmother's belongings. The letter paper was yellowed, but his name was written on it: personally signed by Chen Huaian. There was only one sentence in the letter - "If she comes to you, don't let her go back." That night, Lin Wan appeared at the door of his house, soaked to the skin, holding two small yellow croakers and half a secret letter in her hands. She said that she came from the 38th year of the Republic of China and had to go back and send a list, otherwise the entire underground line would be exposed. Chen Huaian didn't want to believe it, but the old letters, old photos, and the secret codes left by his grandmother all matched. He helped Lin Wan buy medicine, translate telegrams, and look for traitors, but found out that his grandmother had concealed a truth: Lin Wan was not the first person to travel through time, and she would never be the last.
