Snelgrave, an English slaving captain who worked the Guinea coast in the first decades of the eighteenth century, sets down what he saw there for readers at home and, pointedly, for the London merchants he addresses in his dedication.

The longest section recounts the Dahomean king's overthrow of the kingdom of Whydah and the author's own journey inland to the victor's camp, where captives were put to death in ceremonies he describes at length. Other parts explain how Africans came to be sold into bondage, count the numbers shipped annually to America, and describe revolts aboard the ships he commanded; a further narrative tells of his capture by pirates in 1719. His preface anticipates disbelief, citing witnesses then living in London who could confirm the sacrifices and the cannibalism he reports.

The shorter sections began as an answer to a friend who doubted whether the trade was lawful. Snelgrave defends it, then leaves the reader to judge.