The group eventually crash-lands on a cliff-bound, volcanic, unknown (and fictitious) island, located in the South Pacific.

With the knowledge of the brilliant engineer, the five are able to sustain themselves on the island, producing fire, pottery, bricks, nitroglycerine, iron, a simple electric telegraph, and even a seaworthy ship.

The mystery of the island seems to come from periodic and inexplicable deus ex machinas: the unexplainable survival of Smith from his fall from the balloon, a box full of equipment (guns and ammunition, tools, etc.

The secret of the island is revealed when it turns out to be Captain Nemo's hideout, and home harbour of the Nautilus.

Captain Nemo had been the savior of the heroes, sending a message about a fellow castaway, torpedoing the pirate ship.