Ex-lovers Do Hyun-Seo and Ji Soo-Ho reunite unexpectedly when Hyun-Seo becomes Soo-Ho's piano instructor. Flashbacks reveal their tumultuous past, while in the present, Soo-Ho's health issues and Hyun-Seo's financial struggles bring them together again. Tensions rise as they navigate their complex feelings and the introduction of a new musician, Kei, who develops feelings for Hyun-Seo.