When Mi-so and Ha-eun first meet in childhood, their lives become instantly intertwined, forming a bond surrounded by happiness and naivety. But as adulthood arrives, alone and together, they are forced to deal with sadness, anger, grief, growth, and most of all, love.

Once known as the frontman of the rock band Ambulance during his college days, Seung-min now lives a quiet life running a small instrument shop. One day, his legendary first love Bo-na, the girl he never even had the courage to confess to before she suddenly disappeared, unexpectedly reappears in his life. From that moment on, Seung-min's heart begins to race again. But as old feelings resurface, he finds himself trapped in an awkward predicament: a secret he must never let his first love discover… no matter what.