Dal mi, who still believes Nam Do san actually wrote her letters fifteen years ago, is determined to find him and prove to her sister that she too lives a good life.

Dal mi meets her mother again for the first time since the divorce. Do San reveals his interest in Dal Mi and decides to keep in touch with her.

Samsun Tech's real office is flooded with potential investors after hearing their company winning the CODA competition. In Jae exposes Do san's real identity to Dal Mi.

It is revealed that Do San had gone into high school at a younger age, but had always humbly made way for his classmates so that they were not scolded by his teacher, and thus he was seen by others as unambitious.

An unknown figure writes the word 'Revenge' on a paper and attaches it to a poster board. The same person ties a flower at a bridge where someone jumped off the bridge there, with Seon Hak witnessing the incident.

Knowing that Dal mi is jealous, In Jae offers her an AI project from her father at the Morning Group. Won Daek asks whether Dal Mi prefers the old Do san (Ji Pyeong 15 years ago) or Do San now.

While Dal Mi is reviewing her proposal written with feedback from Ji Pyeong, she notices that his handwriting is the same as the letters she received 15 years ago. Do-San gets jealous when Ji Pyeong gives him Dal Mi's hair tie to return to her.

Do San admits that he won the high school mathematics Olympiad by cheating. As requested by Won Deok, Ji Pyeong travels back to Seonju to pick up the last letter Dal Mi wrote to him, but she coincidentally shows up and finds out the truth.

Do San finds Dal Mi and they cry together while he explains why he kept lying. Ji Pyeong finally admits that he wrote the letters and confesses his love for Dal Mi.

Dal Mi proposes a self-driving car as their next venture. Meanwhile, Alex hands them a deal to acquire Samsan Tech for three billion, with a contingency that they work for 3 years in Silicon Valley. Ji Pyeong, hearing the news, attempts to stop the deal but he is too late.

Dal Mi applies to be a strategic planning manager at In Jae Company. Ji Pyeong and Do San negotiate with Alex to continue their work with NoonGil.

Dal Mi is accepted into In Jae Company as their COO and three years later, she is working with In Jae to develop a self-driving car.

Dal Mi's autonomous car is about to apply for a permit, but another car named Momo, developed by the Morning Group is revealed to have already obtained a permit.

Ji Pyeong asks Do San to give his letters from Dal Mi back, but he refuses. Do San tells Dal Mi that he volunteered to work on the self-driving car after Dal Mi's idea at their last meeting with Samsan Tech.

Fast forward to 2020, Dal Mi and Do San are still the CEO and CTO of Cheongmyeong Company, respectively. Pictures show them married, signaling that they won the bid. In Jae and Ji Pyeong are also still part of the company, ending with all four on their way to a shareholder meeting.