Ae Rin and Joon Joon move into Bon's house so that Ae Rin can look after him. The four of them have dinner together, and Bon watches them and shows a heartwarming smile. The next day after coming back from grocery shopping, Ae Rin finds out that Bon has left her a note, saying that he will be gone for the time being.

Ae Rin finds out that Bon's birthday is coming up. Meanwhile, Sun Mi suspects her husband of having an affair. The KIS conducts an operation to get to the bottom of it.