Kim Seo Jin and Kang Hyun Chae's perfect life falls apart after their daughter Da Bin goes missing during a charity event. Meanwhile, Han Ae Ri hears devastating news about her mother's condition.
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.
Seo Jin receives a call from the police that the culprit has been caught and rushes to the police station. While helping Seo Jin, Ae Ri receives a call from the hospital regarding her mother.
Unaware that someone close to him is hindering his efforts to bring back his family, Seo Jin desperately waits for Ae Ri's phone call. Ae Ri is unsure about who chased her at Jin Ho's place, and follows the leads she's gathered 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. While talking to Jin Ho, Ae Ri finds out about how her father died.
After tracking down Lee Taek Gyu, Seo Jin is shocked when he confronts a dead body hanging from some bars. Seo Jin continues to look for Kwak Song Ja, Ae Ri's mother, without realizing that he has already found her.
Ae Ri's mother disappears again. Frustrated and desperate, Ae Ri decides to eliminate what might harm her mother, Lee Taek Gyu. Seo Jin stumbles upon a clue that connects the dots between Do Kyun and Taek Gyu.
Ae Ri waits for the phone call, but it never reaches her. Worried that something might've happened to Seo Jin, Ae Ri does everything she can to prevent Da Bin from getting kidnapped. In the middle of everything, Ae Ri gets into trouble.
Seo Jin struggles mentally and physically after the kidnapping attempt on Da Bin. Ae Ri questions whether she should continue to help Seo Jin. Despite the occurrence with Seo Jin, Ae Ri admits that only he can help her find her mother.
Seo Jin realizes that there's a hidden truth behind the Collapse of Taejung Town. Seo Jin begins to unveil the secret and draws near toward the truth. Meanwhile, Ae Ri tries to verify that the person on the phone is the real Seo Jin.
When Seo Jin wakes up in the hospital, he realizes that he's under investigation by the police. After figuring out a crucial piece of the puzzle, Seo Jin heads straight to Ae Ri's mother, only to see an unidentified dead body.
When Seo Jin visits Ae Ri's mother as discussed, Song Ja refuses to help because of Seo Jin's relationship 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 what she gave him to hold onto so that she can stand face-to-face with the real culprit. In September, Seo Jin and Ae Ri start to cooperate to catch Lee Taek Gyu.
Hyun Chae visits Byung Hak to give him what he wants, but ends up putting herself in danger. Do Kyun finds out about Hyun Chae's past and must make a decision.
Ae Ri's death is nearing, but Ae Ri and Seo Jin still struggle to find a way to save her against all odds. Meanwhile, Ji Ah tells Ae Ri that she saw everything. Ae Ri and Geon Wook visit the storage, where they run into Seo Do Kyun.
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.
