So-joon, a time traveler who only cared for himself, saves Ma-rin, a struggling photographer and former child actress, from a fatal accident.

So-joon learns he'll marry Ma-rin in the future, and she mistakes his actions for love as he grows concerned for her as a washed-up former child star.

So-joon learns that he and Ma-rin survived a subway disaster seven years ago and share a secret fate. Du-sik suggests they have a child to change it.

After waiting for So-joon at Namyeong Station, Ma-rin rushes to the ER upon receiving a call where So-joon's bold and relentless proposal begins.

The couple enjoys married life, but still don't know each other well. Ma-rin grows suspicious after finding futuristic items at home.

So-joon is too focused on his future disappearance to open up about his parents' death, while Ma-rin finds a magazine he brought from the future.

So-joon tries to reconcile with Ma-rin, while Mr. Hwang mistakes him and Gi-dung for a couple, which leads Ma-rin to stake out Gi-dung's place.

So-joon asks Ma-rin to wait for the truth and sleep in separate rooms to protect her, frustrating her as she expects them to rekindle their love.

Yong-jin tries to lure So-joon's investors, while Du-sik fails to push him out. Meanwhile, So-joon and Ma-rin enjoy their short-lived happiness.

Ma-rin comes to believe that So-joon is a time traveler. Meanwhile, So-joon gathers help from her and Gi-dung about Seong-gyu's impending danger.

So-joon finds out about his own disappearance from a detective as he travels to the future to find out the truth behind Seong-gyu's death.

Ma-rin is at So-ri's place as she waits for So-joon to reconcile after storming out, while he has to remain cold despite his enduring love for her.

Ma-rin warns her future self to stay away from So-joon, while he avoids the subway for her. Meanwhile, Yong-jin plots to cover up Seong-gyu's murder.

Ma-rin and So-joon believe that Yong-jin doesn't know the truth about So-joon, but Yong-jin's heard everything from the bug he planted at their house.

Yong-jin takes Ma-rin, and So-joon agrees to meet him on the subway. Du-sik rescues her as So-joon confronts Yong-jin, and unexpected events unfold.

Ma-rin sends So-joon a scheduled email, longing for him, while he throws himself onto the tracks to transcend time in hopes of seeing her again.