Every note of the pianist Shen Qingyan is perfect, but no one knows that his hands have been freed from the fire of sin. Detective Gu Linyuan chased him for three full months, and finally put handcuffs on his wrists on a rainy night in the concert hall - and also on his own old wounds that had never healed.
A deal forced the two to coexist: Shen Qingyan infiltrated the criminal organization "Nightingale" as "Qin Key", and Gu Linyuan became his only monitor and guardian. In the safe house, the piano and the gun confront each other, and lies and truth intertwine. He taught him music theory, he taught him to see through disguises; he took bullets for him, and he helped him step off the cliff at the edge of the system.
When the boundaries between the pursuer and the pursued begin to blur, the hidden past gradually emerges: the "keys" that were buried in a sea of fire seven years ago, the last melody of the missing brother, a secret photo of the top police officers... They discover that each other is not only a chess piece, but also the key to unlocking the mystery of each other's fate.
This is a duet played with life. In the gray area of sin and redemption, lies and truth, law and emotion, can two broken souls find their harmony before the final chapter?
"When you stare into the abyss, the abyss stares into you. But what if someone in the abyss lights a lamp for you?"
