Lu Chen is a night-shift leak detector. He finds underground leaks by listening, and hopes this trade will help him land a stable job.
In the early hours of the morning, a work order for an old residential compound leads him to an old pipe that was removed long ago, according to the blueprints.
Water is still flowing through it. A voice comes through the probe: "Don't seal it! There's still someone down there!"
He finds an old well that has just been sealed, only to realize the plea for help didn't come from the present.
He Yan, a water utility dispatch engineer, helps him verify the pipelines and investigate the work order. Following the seals, water flow, and altered records, the two piece together the hidden underground scene bit by bit.
But the voice he hears won't show up in recordings, and the more he hears, the more likely he is to lose the hearing he relies on to make a living.
One old pipe ultimately leads to a pumping station accident from seventeen years ago.
