Fan Ju accompanied Xu Jia, a high-ranking official from the State of Wei, on a diplomatic mission to the State of Qi. Xu Jia suspected Fan Ju of secretly colluding with Qi and reported him to the Wei prime minister upon their return. Fan Ju was unjustly beaten and severely injured. He then changed his name to Zhang Lu and fled to the State of Qin, where he eventually became its prime minister.

Later, Xu Jia was sent on a diplomatic mission to Qin. Fan Ju, disguised as a shabby and dejected poor man, went to meet him. Xu Jia, seeing his miserable state, kindly gave him a silk robe.

However, when Xu Jia later discovered that this 'poor man' was none other than the Qin Prime Minister, he was utterly terrified and repeatedly apologized for his past actions. Fan Ju, however, chose not to harm him.