Ju-won feels exhilarated about going on a date with a boy who is good-looking and smart, but she soon gets disappointed by what he says to her. San-ha and his father are upset by an unwelcome visitor who reminds San-ha of memories he doesn't want to recall. A surprise present from Hae-jun's biological father brings about a conflict between Hae-jun and his colleague.

With Hae-jun's birthday around the corner, San-ha and Hae-jun get into a big fight. To help them reconcile, Ju-won plans to take them to a rail bike. However, many misunderstandings develop as Ju-won collapses from a cold, and rumours between Dal and Hae-jun spread at the school. Meanwhile, everyone gets ready as Yi-hyun plans to join the birthday party.

Hae-jun's mother, Seo-hyun, unexpectedly visits Yoon's Kalguksu to repay her debt, leaving Jung-jae puzzled as to what to do with it. Meanwhile, So-hee goes missing after leaving home to meet San-ha. Her disappearance reignites the unresolved conflict between Moo-sung and Jung-hee, resulting in San-ha's decision to distance himself from the family.