The defeat of the Chinese pirate Shap-ng-tsai (Zhang Kaiping) by forces from the British and Qing empires in the waters of Vietnam is one of the most impressive naval victories of the mid-nineteenth century. Despite the magnitude of the engagement, it has received limited and mostly one-sided analysis. Engaging with a wider array of sources, particularly those from Qing authorities, allows for a more holistic reconstruction of Shap-ng-tsai's defeat and an assessment of its significance. A comparison between accounts by British and Chinese officials reveals discrepancies reflecting the limits of each side's authority at sea and how they used their (mis)understanding of each other to justify killing thousands of pirates in the waters of a foreign state. Anglo-Qing cooperation against Shap-ng-tsai would provide a model for future anti-piracy expeditions and helped improve relations between Britain, China, and Vietnam in the mid-nineteenth century.