The armored cavalry deployed by Huyan Zhuo was impervious to conventional weapons, vulnerable only to barbed lances. Tang Long provided the lance's design, but no one could wield it effectively. He then revealed that his cousin, Xu Ning—an imperial arms instructor—was a master of this weapon, with skills passed down through generations.
To lure Xu Ning to Liangshan, Tang Long devised a plan centered on Xu Ning's most prized possession: a unique, metal-inlaid goose-feather armor, an ancestral treasure he kept in a leather box suspended from his bedroom beam. Tang Long reasoned that stealing it would force Xu Ning to pursue it.
Wu Yong, the military strategist, assigned the task to Shi Qian, renowned for his agility in scaling walls and rooftops. Shi Qian traveled to the capital, located Xu Ning's residence, and discovered that Xu Ning would be on dawn watch the next day.
At the fifth watch, while Xu Ning ate in the kitchen, Shi Qian slipped inside. After Xu Ning left, Shi Qian entered the bedroom. When Xu Ning's wife heard noises from the beam, Shi Qian mimicked the squeak of a rat, deceiving her into returning to sleep. He then seized the armor and escaped.
Upon discovering the theft, Xu Ning, guided by Tang Long, chased after Shi Qian all the way to Liangshan Marsh. Persuaded by the leaders there, he joined their ranks. Later, using his expertise with the barbed lance, Xu Ning successfully defeated Huyan Zhuo's invincible armored cavalry.