A mysterious and highly successful hitwoman in Hong Kong is paid to assassinate top-level crime bosses. After beginning a relationship with a noodle vendor, she decides to travel to South Korea to complete one last job. Unfortunately, the dead man’s bodyguard is out for revenge.

After being involved in a car accident, Si-hyun is left with no memories of the accident or her past. The accident causes her to see sounds in color which is often disorientating, forcing Si-hyun to protect her ears. She encounters Ji-won in the hospital and moves in with her when she is later discharged. Upon hearing Si-hyun humming a strange melody in her sleep, Ji-won’s brother, Woo-hyuk, writes it down as a score and gives it to her, hoping that it would help her remember something of her former life. Meanwhile, Jee-il, a failed songwriter stumbles upon this score and offers to find the melody. They embark on a healing journey as they collaborate to complete Si-hyun’s melody.