The spring Seo Dal-mi lost everything, Nam Do-san's letters kept her company. Fifteen years later, she needs him by her side to prove Won In-jae wrong.

To preserve Dal-mi's past and to support her future, Choi Won-deok asks Han Ji-pyeong to pull off an impossible task.

Ji-pyeong scrambles to transform Do-san into the man of Dal-mi's dreams. A rude awakening prompts In-jae to close one door and open another.

Despite differing pasts, Dal-mi and In-jae fight for their dreams at the same starting line. Ji-pyeong sets out to protect Dal-mi and help Do-san.

In-jae uses lessons from her father and stepfather to her advantage. A clash over company shares tests Dal-mi, who turns to Ji-pyeong for advice.

Grappling with his feelings for Dal-mi, Ji-pyeong avoids her. Do-san's knowledge of Won-deok's condition inspires a business idea for Samsan Tech.

Devastating news gives Dal-mi another reason to make the app a success. Won Du-jeong's plan to teach Do-san and Dal-mi a lesson backfires.

Do-san and Ji-pyeong struggle to bear the weight of their untold truths. Doubts and a mix-up lead Dal-mi to the place where it all started.

Ji-pyeong gives Dal-mi long-awaited answers and a confession. Seeking success on his own terms, Do-san considers a golden opportunity.

Kim Yong-san forces Ji-pyeong to reflect on his past remarks. In-jae and Dal-mi's companies showcase rivaling programs using the same technology.

Alex Kwon shows his true colors, proving Ji-pyeong right and fulfilling Samsan Tech's worst fears. Do-san tells Ji-pyeong about Won-deok's health.

Dal-mi and In-jae's self-driving car is hit by a ransomware attack. Samsan Tech founders return after a successful three-year stint in San Francisco.

Tasked with recruiting top developers into her company, Dal-mi pitches her idea at Samsan Tech. Do-san gets away to clear his head.

Jung Sa-ha and Lee Chul-san begin dating in secret. A boozy, heartfelt conversation with Do-san helps Ji-pyeong make a decision about Dal-mi.

Do-san and Dal-mi envision new goals for their future. Ji-pyeong finds a way to pay forward his gratitude for Won-deok. In-jae returns to her roots.