Kim Soo-hyun is a mother whose young daughter Han Saet-byul gets kidnapped and murdered. Discovering a miraculous ability to go back in time exactly two weeks before the event, Soo-hyun is determined to expose the kidnapping plot and save her daughter before she dies all over again. Helping her is Ki Dong-chan, a former cop turned private investigator out to prove the innocence of his mentally challenged brother, who is falsely accused of murdering Dong-chan's ex-girlfriend.

After San Francisco suffers a week of terror at the hands of a serial killer ending with the death of Laura Price’s eight-year-old daughter Serena, Laura falls into a dark depression and attempts suicide. Next thing she knows, she’s waking up before that week, whereupon she teams up with ex-police detective Nico Jackson (who also got thrown back in time), hoping to change the week, catch the killer, save Nico’s brother’s life, and save Serena—all in a mere nine additional episodes.