A serious water leak suddenly breaks out at a hotpot restaurant on the ground floor of an aging mixed-use building. The owner, Zhou Dafu, mistakenly blames his upstairs neighbor, and a neighborhood confrontation is about to erupt. Ding Quan, a professional leak detection technician, steps in at a critical moment to investigate. With the help of the owner's daughter, Zhou Xiaoyun, he analyzes the water quality and determines that the hidden leak is not what it seems. Facing agitated business owners, a tangled network of concealed pipes, and the danger of the old building sinking, Ding Quan promises to eliminate the threat within a strict deadline. In the darkness of the night, he uses acoustic technology to penetrate layers of noise and vows to identify the true source of the leak before the underground currents bring the entire building crashing down.