Following the setback described at the conclusion of The War of the Worlds (1898), H. G. Wellss account of the Martian invasion of Earth, the survivors among those Martians who landed near New York retreat into space, destroying the city as they blast off. Thomas Edison examines various technological artifacts left behind by the invaders and deduces the principles involved in their operation. This allows him to produce his own designs for spaceships, powered by antigravity devices, and for new weapons. The latter are disintegrator rays more powerful than the Martians own heat rays.
After the test flight of Edisons prototype spaceship, Earths telescopes reveal new activity on Mars. A conference of world leaders puts together a $10 billion war chest so that a preemptive strike can be launched. Edison is awarded a contract to construct a fleet of spaceships and a vast arsenal of disintegrator rays.
The passengers in Edisons fleet include many of Earths leading scientists, such as Henri Moissan, Sylvanus P. Thompson, and Lord Kelvin (William Thomson).
When the Earth ships arrive in Martian local space, they are faced by a huge fleet of defenders, and immediate engagement is judged unwise. An expedition to a Martian asteroid mine discovers vast reserves of gold, and a subsequent descent to the planets surface leads to the discovery of a human girl named Aina. Her presence there is explained by the fact that the Martians had invaded Earth before, nine thousand years ago.
Aina is now the last human on Mars, the Martians having massacred the rest. She advises them that the Martians are too powerful to be defeated in battle, but that if the canals that distribute water to their cities were to be sealed at the points where they collect the tidal waters of the oceans, there would be a devastating flood. Following this plan, the Earthmen contrive the wreckage of Martian civilization but then must face the vengeful attacks of the Martian ships. Edisons fleet is reduced by half, but the Martians eventually capitulate.