Zhang Lu had inherited control of the Celestial Masters religious group upon the death of his father, Zhang Heng, and therefore became its third leader (the first was Zhang Daoling).

The religion enjoys its greatest popularity in Yi Province (present day Sichuan), but when Zhang Lu takes control of the group, it is being challenged in the area by a shamanistic religion led by Zhang Xiu (no family relation to Zhang Lu, or to the contemporary minor warlord of the same name).

Against this background, both Zhang Lu and Zhang Xiu are abruptly ordered by Liu Yan, Governor of Yi Province, to go together to attack the forces of the official Han governor of Hanzhong, Su Gu, and take over his territory.

However, having his own designs, Zhang Lu kills Zhang Xiu and absorbs his armies and religious followers into his own group before he departs for the campaign against Hanzhong.