Today, Soo-min takes bass guitar lessons from his dad. Soo-min who hates playing the bass rebels against his father as if he ran out of patience. At that moment, the whole world stopped, then Mezzo and Alto appeared. Knowing that the walls between the music and real world collapsed due to the sound of the bass played with a bad heart and he could no longer hear his father's voice, Soo-min went to the Music Country with Mezzo and Alto to solve the situation...