This paper relies on the narrative of a renowned historian of Qing law from China mainland who has been called by Hong Kong High Court in 2007, to witness as an expert in “Chinese customary law.” At the opening of the trial, he recognized one well-known and estimated colleague from Taiwan in the expert engaged by the other party. During one week, these two legal historians called up a vast array of knowledge in Chinese history, culture, and law, to ensure the triumph of their party. The contest opposed the representatives of two branches of a same lineage who claimed their right to manage the lineage common wealth. As both were collaterals with dubious link with the original lineage, experts engaged in sophisticated arguments to make their cause prevail. Successively were adduced lineage registers the tabooing of fathers and emperors' personal name in the Chinese tradition, the degree of kinships as represented by “mourning charts” included in the Qing penal code. Even though it was “privately settled” before any judicial decision, this case raises questions on the very nature of “Chinese customary law”, and the role of “cultural expertise” at Common law in a Chinese environment.