In the Qing Dynasty, the emperor, concerned about the growing influence of the Ming loyalists, assigns a skilled martial artist, Wei Fung, to infiltrate and uncover their secrets. Disguised as a tutor, Wei Fung infiltrates the influential Tien family, suspected of harboring Ming sympathizers. Upon arrival, he wins the trust of the family by teaching their daughter, Chi Chi, with whom he develops a close bond. Wei Fung observes the family's activities closely but finds himself torn between his mission and his emerging feelings for Chi Chi. He soon discovers that not only does the family have ties to the Ming rebels, but they are also adept martial artists intent on safeguarding their interests.

As Wei Fung delves deeper into his mission, he faces moral dilemmas about loyalty and love. His skills are tested when members of the family grow suspicious of his true identity. Battling with his conscience and the martial prowess of the Tien family, Wei Fung starts adopting new combat techniques inspired by observing a praying mantis. These techniques lead to developing a unique fighting style that merges with traditional Shaolin influences. Sensing impending danger, Wei Fung must navigate his dual life and make pivotal decisions at a crucial juncture. The narrative crescendos toward an inevitable clash between allegiance to the emperor and personal bonds, with Wei Fung standing at the crossroads of duty and desire.