Blood River

"The Dark River" is a secret assassin organization formed by the Su, Xie, and Mu families, led by the Grand Elders. When the Elders fall critically ill from a mysterious poison, the families seize the chance to rebel. Su Mu Yu, leader of the Spider Shadow guard, enlists the divine healer Bai He Huai from the Medicine King Valley to save the Elders while defending them from attacks by rival assassins.

(Source: MyDramaList)

~~ Adapted from the novel "Tales of Dark River" (暗河传) by Zhou Mu Nan (周木楠).