Reign of Assassins takes place in the year 428 AD, following the story of Bodhi, a prince from southern India who becomes a Buddhist monk and travels to China. He becomes known as a master of martial arts, but after his death, his remains mysteriously disappear. Rumors spread that his bones are infused with an endless power that could be used to conquer empires.
Centuries later, the Dark Stone is a notorious group of assassins, with its top assassin being Drizzle (played by Kelly Lin). Her latest mission is to assassinate Lord Jung, a high-ranking official. However, her life takes a turn when she accidentally falls in love with a Buddhist monk named Turquoise (played by Leon Lai). Turquoise tries to persuade her to change her ways and leave behind her life as an assassin.
Drizzle ultimately decides to leave the life of an assassin and escapes from the Dark Stone. She takes Bodhi's remains, which she had acquired, and hides them in a safe place at the Yuangue Temple. She chooses to let go of her life as a killer and leave the world of power struggles behind for good.