While on patrol duty, EU sergeant Ling Sun-fung and her team are called to assist a criminal chase. A gun battle erupts and Sun-fung loses her father, who dies from a stray bullet to the head. Sun-fung continues the pursuit, but a strange natural phenomenon suddenly turns her away, taking her back to April 1—three days prior to the incident. Realizing that she has travelled back in time, she uses this opportunity to save her father's life. Village chief "Ditch", an informant for the ICAC, discovers Sun-fung's special ability and teams up with her to investigate a corrupted cop. Unfortunately, their persistent disruption to the timeline causes severe butterfly effects, with unsettling consequences..