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 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.
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.
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.
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 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.
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.
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.
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.
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.