AllMovie

The offices of the Daily Planet are visited by a man named Henderson. He tells the assembled that he is an explorer, as is his father, who has been missing for some time. Henderson wants to launch an expedition into the deep, mysterious caverns that his father was exploring when he disappeared, and he wants the Planet to finance it. Reporters Lois Lane and Clark Kent join the adventurer, with Lois to travel immediately with him down a river into the caverns, and Clark to join them via a separate boat. Lois and Henderson find land and disembark, but their boat slips away and crashes into a cavern wall, where it explodes. They are then captured by some fierce creatures, half-bird, half-man, who plan to sacrifice them by throwing them into a pit of fire. Clark, who had heard the earlier explosion, discovers what is going on and switches to his alter ego, Superman. Superman quickly mops up the birdmen, saves Lois and Henderson, and seals up the caverns leading to the birdmen's land. At the end of the film, editor Perry White burns Lois and Clark's story, saving he can't print it because it is too unbelievable.