Everywhere, anywhere, nowhere, all at once, seven women who were once collectively known as 하트라인 (Heartline) or HTL are drawn back together by fate. It's 2034, and as their twelfth anniversary approaches, (if they are still together) they receive an invitation to reunite on a popular show. Their sudden rise and sudden fall left a trail of unspoken words and unresolved emotions. Now, they must navigate the echoes of their past to find harmony once more. Will the bonds of friendship and music that once united them be enough to rekindle their dreams?