基隆有位讀書人叫李明，到府城考試沒考上只好回家。途中在稻田旁的大樹下休息時，看到有隻田螺從殼裡爬出來要到水裡產卵，殼很輕一下子就被風吹走了，李明好心幫田螺把殼撿回來，結果田螺居然在田埂上寫了二十個字：「龜橋不夜宿，油手不洗身；蒼蠅吃筆尾，八堵黃阿坤。」李明就把字背起來。
黃昏時李明來到龜橋村，一想到田螺寫的字「龜橋不夜宿」，又繼續趕路到隔壁村，第二天吃早飯時，聽到老闆說：「昨晚半夜山洪暴發把龜橋村淹沒了，沒有人逃出來。」李明心想：「田螺救我一命。」
到了五堵時，只剩二十多公里就到家，不過天已經黑了，加上又累又髒，李明決定到客棧休息，天亮再回家。店小二對李明說：「平常這個時候是老闆在洗澡，今天他很忙，你先洗吧！」
李明脫衣服時，不小心把浴室的油燈打翻了，滿手都是油，又想起田螺寫的字「油手不洗身」，便急忙跑出來說：「我不洗了。」老闆娘剛好經過，不想浪費熱水，就摸黑進去洗澡。後來老闆去洗澡時，看到老婆頭破個大洞倒在地上。
李明被當成兇手，縣官拿起筆正要寫死罪時，飛來一隻蒼蠅停在筆上，趕了三次都飛回原地，縣官覺得奇怪，李明趕緊說出發生的事，以及田螺寫的字，縣官馬上派人去八堵查。果然捉到一位叫黃阿坤的屠夫，屠夫立刻承認是自己暗戀老闆娘，而計畫殺掉老闆，沒想到殺錯人，李明便無罪釋放。
There was once a scholar called Lee-ming who lived in Keelung. He went to Tainan to take an exam, but he didn't pass the exam and had to go home. Along the way home, he decided to take a rest under a tree. He saw a snail crawl out of its shell to lay eggs in the water. Its shell was very light and the wind blew it away. Lee-ming picked up the shell and returned it to the snail. To his amazement, the snail left a string of words on the field embankment. “Don't stop at Guei-Chiao, don't take a bath if your hands are oily. A fly rests on the tip of a pen, A-Kun Huang of Badu is the one you seek.” Lee-ming memorized these words and went on his way.
In the evening, Lee-ming arrived at Guei-Chiao village. He remembered what the snail told him, and did not stop to rest. He stopped at the next village instead. As Lee-ming ate breakfast the next morning, he heard the innkeeper say, “There was a flash flood at Guei-Chiao village last night. No one made it out alive.” Lee-ming thought to himself, “The snail saved my life!”
When he got to Wudu village, he was only twenty kilometers from home. But it was getting dark and Lee-ming felt tired and dirty. So, he decided to find a place to spend the night and set off for home the next day. The innkeeper's assistant said, “My boss usually takes a bath during this hour, but since he is busy today, you can bath first!”
While he was in the bathroom, Lee-ming accidentally knocked over the oil lamp as he was taking off his clothes. His hands were covered in oil. Suddenly, he remembered what the snail told him, “Don't take a bath if your hands are oily”. So, he quickly got out of the bathroom and told the innkeeper's assistant, “I don't think I'll take a bath tonight.” The wife of the innkeeper happened to pass by and heard what Lee-ming said. She didn't want to waste the hot water, so she decided to bath in the dark. Later on, the innkeeper found his wife lying dead on the floor with a hole in her head.
Lee-ming was suspected of murder, but when the magistrate raised his pen to sentence Lee-ming to death, A fly rested on the tip of his pen. The magistrate chased the fly away three times, but it always flew back. The magistrate sensed something was wrong, and Lee-ming quickly told the magistrate what happened, including what the snail told him. The magistrate sent his men to Badu, and sure enough, they caught a butcher by the name of A-Kun Huang. The butcher confessed that he secretly loved the innkeeper's wife, and that he planned to kill the innkeeper that night. But the bathroom was dark and he killed the innkeeper's wife by mistake. Upon hearing this, the magistrate set Lee-ming free.
