'Number One Under Heaven') is a Chinese wuxia television series directed by Deng Yancheng and Wei Liyuan, starring Roger Kwok, Li Yapeng, Wallace Huo, Michelle Ye, Damian Lau, Tammy Chen, Gao Yuanyuan and Eva Huang.

Heaven Number One is the calm and cool-headed Duan Tianya, who was raised as Zhu Wushi's godson and sent to Japan to learn ninjutsu from the Iga School.

In his quest for vengeance, he masters a powerful but highly perverse skill, and finds himself falling under its evil influence — to the point where he loses control of himself and starts to indiscriminately kill anyone who tries to stop him.

The secret service is in an ongoing political rivalry with the Eastern Depot, another imperial spy agency led by the eunuch Cao Zhengchun.

The Emperor knows that Zhu Wushi and Cao Zhengchun are equally influential in politics, so he has been pitting them against each other in order to prevent either side from gaining too much power.

All these years, he has been secretly plotting an elaborate scheme to usurp the throne from the Emperor and he is now in the best position to do so; the four agents are merely pawns in his quest for power.