Set in the late Tang Dynasty during Emperor Wenzong's reign, powerful eunuchs control the court. An attempted coup to overthrow the influential eunuch Qiu Ziliang fails, leading Qiu to order the massacre of Prime Minister Wang Yang’s family. Two granddaughters escape, but they are separated. Seven years later, the new emperor, Qi Yan, establishes the Purple Clothes Bureau to confront his godfather, Qiu Ziliang. Now grown, the sisters return under new identities: Qiu Yanzhi as Qiu Ziliang’s adopted daughter and Chen Ruoyun as Qi Yan’s sword-bearer. Although on opposing sides, both seek to dismantle Qiu Ziliang’s power and restore balance to the Tang Dynasty.
