In Chocolate Islands: Cocoa, Slavery, and Colonial Africa, Catherine Higgs traces the early-twentieth-century journey of the Englishman Joseph Burtt to the Portuguese colony of Sao Tome and Principe-the chocolate islands-through Angola and Mozambique, and finally to British Southern Africa. Burtt had been hired by the chocolate firm Cadbury Brothers Limited to determine if the cocoa it was buying from the islands had been harvested by slave laborers forcibly recruited from Angola, an allegation that became one of the grand scandals of the early colonial era. Burtt spent six...