"In 2019, our city witnessed a serial murder case that claimed seven lives. You were the seventh victim." In 2019, a major serial murder case occurred in Jielu City, resulting in seven deaths. Years later, Li Yunshan, a survivor of the case, remains haunted by the tragedy. His beloved girlfriend was the seventh victim. By chance, he obtains a phone capable of bridging past and future, and unexpectedly connects with Xu Sixian before her 2019 murder. To prevent the tragedy from repeating and save innocent lives, the two embark on a time-spanning pursuit to track down the killer.