As Zhu Huiyin served as the Governor of Guangdong, the region was plagued by a spate of unsolved homicides. Traveling merchants were frequently targeted, vanishing without a trace, their bodies never recovered. In total, over a hundred such cases had accumulated. Zhu Huiyin was deeply distressed, having exhausted every known method to apprehend the true culprit. In desperation, he fasted, purified himself, and proceeded to the City God Temple to offer prayers.

That night, as Zhu Huiyin retired to bed, he dreamed of an official-looking man, clad in robes and holding a hù tablet, who approached him with an ethereal grace. Assuming him to be a court dignitary, Zhu Huiyin inquired, "May I ask what post you hold, esteemed Sir?" The man replied, "I am Liu, the City God." Zhu Huiyin was overjoyed, recognizing this as a divine manifestation, and asked, "What counsel do you bring, my Lord?" The spirit responded, "Snow hanging at the temples, clouds forming at the horizon, wood adrift on the water, a door set into the wall."

Zhu Huiyin frowned in deep contemplation. After a long pause, realization dawned: "Snow at the temples signifies the character 'Old' (); clouds at the horizon, the character 'Dragon' (); wood adrift on the water, the character 'Boat' (); and a door set into the wall, the character 'Door' (). Together, does this not spell 'Old Dragon Boatman' ()?"

It turned out that in the northeast of Guangdong province, two rivers—one called Xiaoling and the other Languan—both originated from Laolongjin and flowed all the way to the South China Sea. Due to the convenience and low cost of water transport, most visiting merchants heading to Guangzhou preferred passage via these routes.

With this insight, Zhu Huiyin immediately summoned his yamen runners, imparted his instructions, and commanded them to proceed to Laolongjin to apprehend the boatmen. They arrested over fifty men in succession, and upon rigorous interrogation, all confessed. These men, under the guise of ferrying passengers, would lure merchants onto their boats, use knockout drugs or soporific smoke to incapacitate them, steal their valuables, and then slit their bellies, load them with heavy stones, and sink the bodies in the river.

With the injustices rectified and the truth revealed, the populace rejoiced, composing ballads that celebrated Governor Zhu's deed and spread his renown far and wide.