During the Civil War five survivors escape from a prison camp in Richmond, Virginia by hot air balloon and find themselves on an uncharted island in the Pacific. Far from any kind of known civilization, the island is inhabited with carnivorous monsters, bloodthirsty pirates, and mad genius Captain Nemo, who lives on the island for his own secretive ends.
Captain Nemo is a madman, genius and legend in the annals of war. In his impenetrable compound, he and his manservant Joseph work toward an inconceivable goal: to build an incalculably destructive bomb, hoping it will end war forever. He wants Cyrus, a gifted engineer, to help him. Together. he hopes they can embark into explosive infamy on his famed submarine, Nautilus.
When Cyrus refuses to work with Nemo, the latter casts his ill-fated guests back into danger, where they are certain to meet their doom. Already in great peril roaming an island teeming with carnivorous beasts, they are further threatened when Bob Harvey and his band of bloodthirsty pirates arrive seeking treasure.