John Hanning Speke’s discovery of Lake Victoria in 1858 while on a quest to find the source of the Nile elevated him to the pantheon of heroes of African exploration, alongside David Livingstone and Henry Morton Stanley. But historians have ignored the part played by the Welsh mining engineer John Petherick in the discovery, largely because Speke branded him a slave trader. In this first biography of Petherick, John Humphries explores whether Petherick was truly a rogue, as he is often portrayed, or the victim of a conspiracy that destroyed his reputation and denied him credit for one of the greatest feats in African exploration.