Curiosity leads Hae Jun to discover a time machine and begins his adventures across time; Yoon Young works as an editor for a famous writer and neglects her mothe until she receives a shocking phone call.

Despite her confusion about the current situation, Yoon Young recognizes a small possibility of altering the future after a chance encounter with Soon Ae; Yoon Young learns about the mistreatment that Soon Ae is facing from the other kids.

Yoon Young is able to enter school thanks to Hae Jun's help; as soon as she begins her classes, she realizes that one of her classmates was the future Ko Mi Sook.

With the day drawing closer, Hae Jun experiences mounting anxiety over the possibility of failing to prevent the murder; while the school is on a field trip, a new student teacher is introduced, whom Yoon Young finds strangely familiar.

Now that Yoon Young has developed trust in Hae Jun, she believes it's crucial to disclose her relationship with Soon Ae and Hee Sub to him; Hae Jun finally comprehends the reasons behind Yoon Young's fixation on Soon Ae.

Hae Jun feels it's unnecessary to share what he saw with Yoon Young, complicating the situation; meanwhile, Yoon Young is surprised by Soon Ae falling for Hee Sub despite her attempts to break them apart.