By 1808, both Britain and the United States had passed laws outlawing the transatlantic slave trade. Yet the trade covertly carried on. In the summer of 1813, in what is now Liberia, a compound of slave pens was bursting with sick and anguished captives, guarded by other African slaves. As a British patrol swooped down on the illicit barracoon, the slavers burned the premises to the ground, hoping to destroy evidence. This story can be told...