Contains spoilers for this episode and earlier episodes.
Ji-pyeong admits that he wrote Dal-mi's childhood letters at Won-deok's request and recruited Do-san to continue the deception. Dal-mi questions whether anything in the new relationship was real, including Do-san's feelings. She withdraws from both men and struggles to face her grandmother's part in the lie. Samsan Tech must still prepare for Demo Day, so she keeps working despite the personal breach that now runs through the company.
Ji-pyeong tells Dal-mi that he likes her, while also defending the sincerity of Do-san's affection. Do-san tries to recover the confidence of their first meeting by changing into a suit, but reaches the park after she has left. His father also needs support during a dispute over work threatened by new technology. Do-san asks him to keep fighting and tries to rebuild their relationship without the impossible standard of being his father's flawless son.
Dal-mi discovers that In-jae claimed to be the girl whose swing inspired Sandbox. She confronts her sister, and Do-san supports her without pretending to be the person from the letters. He reminds Dal-mi that getting Samsan Tech into Sandbox was her achievement. Meanwhile, Yong-san confronts Ji-pyeong about his brother's death and reveals the anger behind his own participation in the program. Unwilling to rely on Ji-pyeong as a fallback investor, Do-san approaches Alex and accepts his offer.