As the director of Yoojoong Constructions, Seo Jin hosts a violin recital where his wife performs in order to enhance the image of the company. However, the concert hall turns into chaos as their daughter Da Bin goes missing. Meanwhile, Ae Ri takes her mom to the hospital for surgery after getting a call that they have found a heart donor for her mom.

While Seo Jin hands out flyers to find his missing daughter, he gets a phone call from the kidnapper. Meanwhile, after Ae Ri’s mom goes to the hospital for the transplant surgery, she hears devastating news from her doctor that her mom’s condition is too bad to have heart transplant surgery and the donated heart will go to the next person on the list.

When Ae Ri goes back to the hospital, she finds that her mom is gone. Meanwhile, Seo Jin realizes that he is living a month ahead of Ae Ri. In order to save his wife and daughter, Seo Jin calls Ae Ri to tell the truth, but Ae Ri doesn’t believe Seo Jin.

Ae Ri asks Seo Jin to prove himself being in the future. He shares the winning numbers of the lottery, about her murder of Geon Wook, and in return asks her a favor. As unbelievable as it may seem, Ae Ri slowly starts trusting Seo Jin and visits his office in her time as he requested.

Seo Jin receives a call from the police that the culprit has been caught. When he rushes to the police station, he finds out that it was the very man who was protesting alone in the lobby of Yujung Constructions. Although it’s too late to save Da Bin, he believes he can still save her.

For a minute over the phone, Seo Jin informs Ae Ri of the name of the kidnapper and asks for help. While helping Seo Jin with the matter, Ae Ri receives a call from the hospital regarding her mother’s belongings. At the hospital, she finds out how Kim Jin Ho is also related to her mother’s disappearance.

When Ae Ri knocks on Kim Jin Ho’s door, Jin Ho panics and tries to force her into the house. That’s when Geon Wook shows up to save her, and the two start running away. After the incident, Ae Ri updates Seo Jin about the happening and tries to find the reason why she was chased.

Without knowing that someone close to him is hindering his efforts to bring back his family, Seo Jin desperately waits for Ae Ri’s phone call. At the same time, being unsure of the person who chased her at Jin Ho’s place, Ae Ri follows whatever lead she has acquired so far.

Although Seo Jin realizes that there must be more people involved in the kidnapping of his daughter, he still needs more information to be certain. Meanwhile, it turns out Hyun Chae was having an affair. While talking to Jin Ho, Ae Ri finds out about how her father met his death.

Seo Jin finally gets a phone call from Ae Ri. When he finds out that one of his close people tried to kill Ae Ri a while ago, he decides to persuade Jin Ho into helping him. However, Seo Jin doesn’t have a clue who else is involved in this matter.

After tracking down Lee Taek Gyu with a secretly planted GPS device, Seo Jin is shocked when he confronts a dead body hanging from some bars. After the incident, Seo Jin continues to look for Kwak Song Ja, Ae Ri’s mother, without realizing that he has already found her.

Although he realizes that the dead body is of Ae Ri’s mother, Seo Jin decides to keep his mouth shut, but instead, he informs Ae Ri about the time and place of her death. Meanwhile, Seo Jin gets surrounded by a group of policemen under the suspicion of Kwak Song Ja’s murder.

Kim Seo Jin hears about Kim Jin Ho’s suicide but goes on to further investigate the situation. Meanwhile, Ae Ri’s mother disappears again. Frustrated and desperate, Ae Ri decides to eliminate what might harm her mother, Lee Taek Gyu.

While Do Kyun is dissatisfied by the fact that Taek Gyu killed Kim Jin Ho, Seo Jin stumbles upon a clue that connects the dots between Do Kyun and Taek Gyu. With the help from Ae Ri, Seo Jin continues with his investigation and tracks down Da Bin’s teddy bear with a location tracker.

Ae Ri waits for the phone call, but it never reaches her. Worried that something might have happened to Seo Jin, Ae Ri does everything she can to keep Da Bin from getting kidnapped. In the end, Ae Ri, Geon Wook, and Soo Jung plan to sneak into the charity event in order to protect Da Bin. While doing so, Ae Ri gets into trouble.

Ae Ri is arrested as a kidnapper, and Seo Jin from the same timeline misunderstands her as a threat. Feeling frustrated, Ae Ri regrets the fact she gave it all to help Seo Jin. Not knowing this, Seo Jin refuses her request for leniency. However, his memories begin to surface.

Seo Jin struggles mentally and physically after what he considers a kidnapping attempt by Ae Ri. At the same time, Ae Ri questions herself whether she should continue to help Seo Jin. While both are on the verge of losing mutual trust, Hyun Chae goes through Seo Jin’s belongings.

Despite the misleading, discouraging happening with Seo Jin, Ae Ri admits that only Seo Jin can help her find her mother. At the memorial park, while Seo Jin is making a presentation regarding the Taejung New Town Project, Ae Ri runs into Seo Do Kyun, who later hears his own voice over Ae Ri’s phone call.

Seo Jin visits Taejung Town Collapse Victim’s Association. He finds out that his father is not the kind of person who would commit suicide and leave his son alone. He decides to investigate the collapse incident further for himself.

Ae Ri feels perplexed at Seo Jin’s unfamiliar reactions. She feels something fishy and tries to confirm that the person with the phone is Seo Jin. Hyun Chae also feels strange at Seo Jin’s different behavior.

When Seo Jin wakes up in the hospital after the accident, he realizes that he’s being investigated by the police. That’s when Seo Jin receives a secret note that asks him to come out to the hospital parking lot. At the parking lot, Seo Jin encounters an unexpected visitor.

Seo Jin cooks up a scheme so that he can grasp the situation better. While doing so, Seo Jin lets Ae Ri from her timeline know that there has been an accident in which he lost Da Bin and Hyun Chae. After figuring out a crucial piece of the puzzle, Seo Jin heads straight to Ae Ri’s mother, only to see the police carrying someone's dead body out of her house.

The dead body turns out to be Ae Ri's. Seo Jin is taken aback when he sees her. Meanwhile, Ae Ri from her timeline realizes that she will die after a month. Knowing her future death, she asks her mother a favor regarding what’s about to happen.

There is nothing more Ae Ri can do to prevent her upcoming death. Meanwhile, Geon Wook decides to cooperate with Seo Jin to save Ae Ri. When Seo Jin visits Ae Ri’s mother as discussed, Song Ja refuses to help because of Seo Jin’s relations with Yujung Constructions. However, this all changes when she talks to Ae Ri from the other timeline over the phone.

Song Ja asks Jin Ho to return to her what she gave him to hold onto so that she can stand face-to-face with Chairman Yu. In September, Seo Jin and Ae Ri start to cooperate to catch Lee Taek Gyu. Meanwhile, Seo Jin heads over to see Song Ja at a hotel to get evidence but finds her missing with traces of blood on the floor.

Seo Jin gets arrested, leaving Ae Ri desperately in need of evidence against Chairman Yu before she meets with Lee Taek Gyu. When she meets with him, he takes her to meet with Chairman Yu at another location. With the location tracker destroyed, Seo Jin gives chase with the police only to find her lying unconscious in the middle of the road.

Seo Jin and Ae Ri succeed in catching Lee Taek Gyu but the future remains unchanged. What is Seo Jin missing? Meanwhile, Do Kyun reveals his true colors to Seo Jin and threatens Seo Jin to give up everything he has. Furthermore, Do Kyun finds out about Hyun Chae’s past and must make a decision.

Hyun Chae visits Byung Hak to give him what he wants but ends up putting herself in danger. Do Kyun starts to worry as Hyun Chae suddenly goes missing. Meanwhile, Seo Jin finds out the truth about the Taejung Town Collapse. Do Kyun and Ae Ri plan to meet up with Jin Ho to collect the evidence.

Ae Ri’s death is nearing, but Ae Ri and Seo Jin still struggle to find a way to save her. Meanwhile, Ji Ah tells Ae Ri that she saw everything. As a result, Ae Ri gets Ji Ah to successfully identify Park Joo Young, which gets Park Joo Young arrested for attempted murder.

Ae Ri is having a hard time locating the package when Ji Ah asks her for her favorite toy. While at the house looking for the toy, she finds out about a storage service. Hoping that this could help her find the package, Ae Ri and Geon Wook visit the storage where they run into Seo Do Kyun. In the end, Ae Ri and Seo Jin agree to go with their last option to save their loved ones.

By sacrificing his life, Seo Jin manages to acquire a voice recording of Chairman Yu’s confession. Now that Seo Jin from a month ahead is gone, Ae Ri and Seo Jin have only one month to save themselves. However, things don’t pan out the way they should.