The Quest team is in Africa, where they plan to launch a balloon to carry a scientific package into the air. But the balloon gets away and is swept to the top of the Devil's Escarpment, a two mile tall rock formation that cannot be climbed. It will take months to build a new instrument package, so the team resolves to fly to the top of the escarpment.
Race delivers Dr. Quest, then returns with the boys, to find that Dr. Quest is missing. His whereabouts are soon revealed, when Race and the boys are captured by the same cavemen -- all of whom work for sinister German Heinrich von Duffle. Worse, Dr. Quest is convinced "von Duffle" is actually escaped war criminal "Klaus", who ran a concentration camp. He'll certainly never let the team escape to reveal who and where he is.
Klaus prepares to leave in the Quest plane, as the Quest team looks for another way out -- and finds it, in the form of passages through the stone that lead to narrow paths outside the escarpment. Klaus tries to eliminate the team with old German grenades, but a miscalculated throw sends him to his doom, allowing the team to escape.