From Introduction:
In the late 1800s the Martian civilization invaded Earth with their various fighting machines and biological weapons of war, the vast majority of them succumbed to the common germs of the Earth, died, and left behind their advanced technology - the tripods with heat rays, flying machines, and other devices.
All around the world, the leading scientists reverse engineered the Martian technology and unlocked the secret of their power: atom-smashing, thermoelectric engine-batteries, powered by the Sun’s cosmic rays. A by-product of the engine is steam (which the Martians infused with toxins and particulates harmful to humans to create the black smoke).
Time passed, and Earth got back to its business as usual; politics and war and exploration and adventures from the streets of London or Moscow to the dark heart of Africa or the gold fields of North America, not to mention the daily ebb and flow of ordinary life - now with amazing machines to aid and assist. Societies abound, some secret, some not, ready to use this new technology to further their agendas.
Regardless of humanities individual pursuits, everyone has an eye trained on the heavens and the red planet next door. Will the Martians invade again, and when? And what of the evidence the Martians also invaded Venus?
There is even some talk of building naval vessels to take humanity to the Moon, and then eventually taking the fight to Mars. Rumors persist...not all Martians, nor their beasts of war, died. Some are said to be in hiding, waiting for the next invasion...
Such is life in the late 1800s.