Behind the iron door of an abandoned hospital examination room hangs a rusty lock that has not been opened in thirty years. Its key has long since been worn smooth, but the echo inside the lock has never stopped.
Three years ago, Chen Mo's older sister, an intern doctor, disappeared here. On her final phone call, all he heard besides her labored breathing was the click of the iron door locking shut. The moment he pries open the examination room to find answers, that sound begins to haunt him. It rings at midnight every day, as if someone is turning a rusty lock beside his ear, drawing closer inch by inch.
In a dusty drawer, he finds a yellowed medical record: "When you hear the lock turning, don't look back." The date on it is the day after the "medical accident" twenty years ago. Everyone who has come into contact with this record has ended up as fresh earth in the nameless graveyard behind the hospital, their bones reeking of rust.
Old Zhou, a retired orderly, is always watching him from the shadows of a general store. He hands him an old key engraved with a blurred name and says, "Some locks are more terrifying open than closed." But Chen Mo can no longer stop. He discovers that his reflection is slowly turning into the person in the medical record's photograph. And on the recording left behind by his sister before she disappeared, amid the sound of the lock, he hears his own voice saying, "Lock it tight. Don't let it out."
When the rusty lock finally turns in his hand, what erupts from the echo is not the truth, but the screams of those buried alive behind the wall twenty years ago. The lock was never meant to keep outsiders out. It was made to imprison the "thing" that crawled off the operating table back then. And he has long since become the new key.
