Hyeong Ju loses one of his closest friends. This is when he receives a phone call from an unknown caller telling him that he can go back a year in time.
The first group of people to go back in time is selected and the reset becomes the reality. However, at the first meeting after the reset, they hear about the death of one of the group members.
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 exactly the same accident that she got into.
The police find the dead body of Yeon Soo at the park where she met with Ga Hyeon on 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.
Ga Hyeon and Hyeong Ju eventually get in touch with Jung Tae and in doing so, they find out about his relationship with Jeung Seok. The more they look into the mysterious deaths of the resetters, the clues direct them toward Lee Shin.
Ga Hyeon and Hyeong Ju are certain that Jung Tae is the bad guy and Jeung Seok is just one of his many victims. However, this all flips around when they come across a conversation between Jung Tae and Jeung Seok.
It turns out that the bouquets were sent by Ms. Song under Lee Shin's order but when Ga Hyeon and Hyeong Ju found out about it, Lee Shin was already gone. What was thought to be an arson was just a mere accident at the flower shop.
Ga Hyeon and Hyeong Ju finally figure out the true meaning behind the message, the date of death. However, this time, no one dies on the date they expected.
Lee Shin shows herself at the café where the resetters were discussing the dead truck driver. This is when Lee Shin reveals the fact that the resetters were all dead in previous resets.
As suggested by Lee Shin, Se Rin tries to flee from Seoul with Young Woong. However, Young Woong leaves Se Rin at the bus terminal to meet Hyeong Ju to file a suit against her.
Ga Hyeon struggles to decide whether to help Se Rin or to ignore her for her deceitful wrong doings. Even before she had time to make a decision, Se Rin is found dead.
It was no surprise when Hyeong Ju finds out Jae Young was with Se Rin hours before she was murdered. Meanwhile, Jung Tae is threatened by Jae Young's father, a nominee for the Minister of Education, to stay low until the hearing is over.
While Hyeong Ju is acting suspiciously for some reason, a voice recording is delivered to the police station. This triggers Ga Hyeon to investigate the voice recording. She concludes that Hyeong Ju could actually be the culprit.
Hyeong Ju feels irritated that Ga Hyeon suspected him of the murder of Jung Tae. Meanwhile, Sun Ho asks Hyeong Ju to explain certain things he's been having a hard time understanding.
Sun Ho turns out to be the murderer who caused the deaths of resetters. However, Hyeong Ju does not have a clue about it and reports every detail of his investigation to him.
Hyeong Ju and Ga Hyeon find out that Sun Ho is the real culprit who is responsible for the deaths of resetters. In fact, they also realize that Ga Hyeon's house is wiretapped by Sun Ho.
Luring Sun Ho into Hyeong Ju's trap was easy, and the police arrest him right after he fires a gun at Hyeong Ju. It seemed as if everything was over, but Hyeong Ju discovers a shocking secret.
Attempting to stop Professor Hwang from making use of the reset for his personal enjoyment, Hyeong Ju dives into his second reset with the help of Lee Shin.
