Slim is a boy whose astronomer father is visiting the country estate of an important industrialist. The industrialist's son, Red, has found two strange animals, and he enlists Slim in a plan to turn the animals into a circus act. The astronomer, meanwhile, tells the industrialist that he has been in contact with space aliens who want to open up their world to interstellar trade. Their world needs help, the astronomer says; ever since the atomic wars that destroyed their old civilization, the world has been regressing. Unless something is done, their culture may be facing total collapse.
The Terran system is growing and expanding all the time. But an old and corrupt Centaurian Empire is holding Terra down, as it encircles the Terran system and will not let the humans grow out of their current empire. For this reason Terra is at war with Proxima Centauri and is trying to find a way of breaking free from the Centaurian's hold upon them.
In the war that results, Terra is continually coming up with new weapons to try and break the Centaurian defenses, but Proxima Centauri is also continually updating its defenses
This is where Thomas Cole, known as The Variable Man, comes in. Cole is a man from the past, from 1913, the time just before the First World War. He is brought into the present (or future depending on perspective) as an accident via a Time Bubble that was used for research about the past. It is discovered that this man has a certain genius to fix things and make things work. This is because he comes out of a period of time when humans had a natural genius and an ability to invent things and to solve problems. It is at this point that the man working on the FTL (Faster Than Light) bomb realizes that The Variable Man is the only person who can make it work.
Written between 1895 and 1897, it is one of the earliest stories that detail a conflict between mankind and an extraterrestrial race. The novel is the first-person narrative of both an unnamed protagonist in Surrey and of his younger brother in London as southern England is invaded by Martians.