The Flying Fox (), also known as The Purple Lightning Sword, is a 1964 Hong Kong wuxia film produced by Gam Wing and directed by Siu Sang.
Wan Liyun, the leader of a martial arts sect, investigates the murder of his uncle Wan Jianfeng, who has been killed by a masked attacker using the Emei Sect's skills. During this time, Wan Liyun meets Di Xiaoqing, a Mongol princess in disguise as a man. After further investigation, he concludes that Yinyang Guaisou, who works for Di Xiaoqing's father Prince Beidi, is the real murderer attempting to push the blame to the Emei Sect. Di Xiaoqing secretly helps Wan Liyun evade danger and ultimately kill Yinyang Guaisou to avenge his uncle.