Pandora In The Congo by Albert Sánchez Piñol

It is 1914. In the heart of the Belgian Congo, Garvey, a bedraggled British manservant, emerges from the jungle. He is the lone survivor of a mining expedition in which both his masters have died, and all of the party's African porters have fled. With him, he carries two huge diamonds. From his prison cell in London, Garvey recounts his horrific and thrilling ordeal. Young Tommy Thomson is assigned to transcribe Garvey's story and only he can untangle the extraordinary mysteries of the Garvey case.