While on patrol duty, EU sergeant Ling San Fung and her team are called to assist a criminal chase. A gun battle erupts and San Fung loses her father, who dies from a stray bullet to the head. San Fung continues the pursuit, but a strange natural phenomena suddenly turn her away, taking her back to April 1st—three days prior to the incident. Realising that she has developed the power to time-travel, she uses her new ability to save her father's life. Unfortunately, her disruption to the timeline causes a chain reaction, with unsettling consequences. Village chief "Ditch", an informant for the ICAC, discovers San Fung's special ability and uses it to investigate corrupted cops, but harbours a secret that bears his true identity. Meanwhile, San Fung discovers that she is not the only person who has developed the ability to travel through time. She learns that her power to change the past does not make her able to control the future.