Five years ago, the provincial criminal investigation detachment rounded up the serial killer "Siren". Criminal psychology profiling expert Lu Yan and his partner Ji Xun pretended to be a couple to perform an undercover mission, but they both lost their memory in the explosion.
Ji Xun forgot his face, but always remembered "there is a person who loves me very much and I love him very much." She was transferred away from the front line and searched all the files privately, just to find that name.
Lu Yan forgot her voice, but subconsciously stood behind her at every crime scene to block the backlight - his body recognized her earlier than his mind.
Five years later, a serial murder case imitating the "Siren" reappeared. The two reunite and work together to solve the case without remembering each other. Every crime scene leaves "flaws" that only the other party can understand - those tacit understandings in muscle memory become the key for them to solve the mystery and find each other.
And the murderer is watching all this from the dark. What he was waiting for was the moment Lu Yan recognized Ji Xun.
"My profile can describe the murderer's desire, but it cannot describe why my heart beats faster for you."
