Three mining employees are marooned in the Sahara after their helicopter crashes in a storm. It had been redirected because it flew into a danger zone for an upcoming nuclear test detonation. They flee the damaged helicopter just before it tumbles off a ledge into a ravine. A shallow cave offers them shelter from the torrential rain that is starting a flash flood in the ravine. Hearing cries for help, they rescue a man from the flooded ravine. He is Tamal, an important Atlantean leader, who takes them through a secret doorway to the lost city of Atlantis. He is the chief advisor of Queen Antinea. Robert, one of the mining engineers, captures the Antinea's fancy. She wants nothing of Tamal any more, declaring her love for Robert. The pilot John meets a grim fate when he attempts to escape by sneaking out just after Antinea has sent for Robert. Zinah, a beautiful slave woman, falls for the third mining crew member, the engineer Pierre. She endeavors to help him escape, knowing a path out of the tunnels. Pierre knows, too, that the atom bomb test is about to commence and will probably destroy the underground city.