Hyeong-ju, while living an ordinary detective life, loses one of his closest colleagues; he receives a phone call from an unknown caller telling him that he can go back a year in time as long as he is willing to do so.

The first group of people to go back in time is selected, and the reset becomes a reality; Hyeong-ju finds himself back in time before when Sun-ho is murdered; Ga-hyeon is back to when she had two healthy legs.

What seemed to be a free opportunity for a better life, sends Ga-hyeon into a downward spiral when she finds her friend, Ju-young, as the victim of the same accident that she got into.

After losing Ju-young from the same accident as hers before the reset, Ga-hyeon decides to find the driver who killed her friend; when Ga-hyeon and Hyeong-ju were on the verge of finding the evidence, they come across the murderer.

The police find the dead body of Yeon-soo at the park where she met with Ga-hyeon the night before; when Ga-hyeon is summoned to be questioned as a testifier, she has no choice but to hide the details regarding the reset.

After the investigation at the police station, Ga-hyeon helps Hyeong-ju track down Bae Jung-tae, who might hold the key to the recent mysterious deaths of fellow resetters.