 Johnny Weissmuller guides Professor Blakely (Selmer Jackson) and his daughter Nora (Angela Stevens) into forbidden Kirundi land, home of the fire-worshipers, in search of missing scientist Ralph Dixon (William M. Griffith). In addition to finding Dixon worshiped as a fire god, they uncover a treasure of sapphires, rout a party of renegade whites and Johnny rescues Nora from flaming death on a ritual altar just before a volcano erupts molten death.