With Hae-joon’s birthday around the corner, San-ha and Hae-joon 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-joon spread at the school. Meanwhile, everyone gets ready as Yi-hyun plans to join the birthday party.