舟山六横岛有个田坳村，村后傍青山，村前临海滩。这里有一对兄弟，大郎和二郎，他们的故事在一个月夜开始了。当他们去海边捉沙蟹埋蕃薯时，一切都显得如此生动。沙滩上密布着沙蟹、红钳蟹，兄弟俩兴奋不已。大郎挥舞扁担，在前面打击，而二郎在后面收拾，他们很快就装满了两箩筐。大郎吩咐二郎先回去挑剩下的，然后他再回来挑。然而，当二郎赶到海滩时，大朗不见了，只留下一片寂静的海岸线和无人的山间。
二朗急得泪流满面，他跑向老公公那里求助。老公公告诉他，有一条千年黑鲨鱼，它曾经残忍地吃掉过他的爷爷和爹爫，说不定大朗也遭遇了同样的命运。这消息让二朗既悲伤又愤怒，他发誓要找到黑鲨鱼并报仇。老公公建议他前往龙山湾寻求龙公主的帮助。
经过多番努力，终于找到了龙潭周围的一座宫殿。在那里，二朗遇到了天仙般的少女——龙公主，她为他的勇气所感动，并送给他一支黄灿灿的龙头金钗，以备将来之需。但当他踏上追杀黑鲨鱼之路时，却发现自己迷失了方向直到 dragon head gold pin suddenly flashed out a golden light, leading him to a path that led to the black shark. With the help of the golden light, he was able to kill the black shark and rescue his brother.
After their victory, they decided to bring back the black shark's body for their village people to use its skin and meat. The dragon head gold pin called upon 18 giant whales to help them drag the massive body back home. Riding on top of these whales, they returned triumphantly.
Their story became a legend in the village, reminding everyone of bravery and loyalty among brothers.
