A Greek fisherman gets caught up in court intrigue in a land of scientific wonders.

Demetrios, a young sailor in ancient Greece, finds an unconscious girl adrift in the Mediterranean. Upon awakening, she informs him that she is the Princess Antillia of Atlantis, and he agrees to take her home. When they arrive in Atlantis, Antillia learns that her father's power has been usurped by Zaren, the minister of war, who plans to conquer the world with a deadly crystal that lies embedded in an extinct volcano. To dislodge the crystal, Zaren has recruited hundreds of slaves, some of whom have been turned into animals by his surgeon. Though Demetrios is also forced into slavery, he wins his freedom when he overpowers a 7-foot man in the Ordeal by Fire and Water. Eventually Zaren succeeds in removing the crystal, but on the day that the great war is to begin, the volcano suddenly erupts. As Demetrios, Antillia, and some of the slaves escape in boats, Zaren turns the deadly rays of the crystal on them. Before he can kill them, however, he is destroyed by his own diabolical weapon. Waves of molten lava pour over Atlantis, and a mammoth tidal wave sweeps over the continent, causing it to sink into the sea. Demetrios, Antillia, and the other survivors sail away in search of a new continent.