In the third century, China was divided into three kingdoms: Wei (wèi guó 魏国) in the north, Shu (shǔ guó 蜀国) in the southwest and Wu (wú guó 吴国) in the southeast. Shu was a weak state.

In the reign of Emperor the Second of the Qin Dynasty (qín cháo 秦朝,221-207 BC), the prime minister Zhao Gao (zhào gāo 赵高), obsessed with ambitions, was planning to usurp the throne day and night. But he did not know how many of the ministers in the court were allowed to be ordered about by him and how many of them were his opponents. So he thought out a way to test how high his prestige among the ministers was and also to find out who dared to oppose him.