This chapter of the main quest begins while you are talking to Fayun in the City of Chang'an. Nobody knows for sure where the telkine went after entering the city. But there is a possibility. The scholars have determined that the last Titan is imprisoned nearby. They fear that the telkine may use the sickle to free him. The exact location of the prison is not documented, but the Yellow Emperor in The Jade Palace on Mount Qiyun knows where it is. So you leave Chang'an through the southeastern breach in the wall, travel to him and get the information. His monologue completes this story chapter and starts the next, Under Wusao Mountain.