The science-fiction novel, published in 1953, is a tale about the extinction of the human race. Beginning in the year 1975, the Americans are competing with Russians to be the first in space travel. The hopes of both countries are dashed, when invaders from another planet occupy Earth. The ships, operated by enigmatic creatures referred to as the Overlords, hover over every major world city.

Five years later, the Overlords become rulers of Earth, turning it into a Utopian paradise. While most humans are happy about the peaceful state of the world, some are discontented about having their personal liberties stripped from them. One such group, the Freedom League, is lead by Alexander Wainwright.

Karellen, also known as the Supervisor of the Overlords, is very secretive about his appearance, and will at first only speak to Rikki Stormgren, Secretary General of the United Nations. Fifty years after Stormgren's retirement, Karellen decides to leave his ship and meet the humans face to face. They are shocked to find that the Overlords are the image of the Devil. While the Overlords keep in contact with humans, they rarely leave their ship, finding the atmosphere and lower gravitational pull uncomfortable.

A party at Rupert Boyce's African home reveals much about his guests. The main attraction is an Overlord named Rashaverak, who is interested in Rupert's collection of books on the occult. Rupert's new brother-in-law, Jan Rodericks, is an aspiring astronomer who is displeased with the Overlords' ban on space travel. Another couple, George Greggson and his girlfriend Joan Morrel, is involved in a syance that leaves them both troubled. Afterwards, the couple marries and moves to an experimental commune.

Meanwhile, Jan stows away on an Overlord's supply ship in an attempt to visit their home planet. While he is away, the world goes through the last stages of its existence. Starting with George and Jean's children, the rest of the world's youth undergoes a metamorphosis that turns them into inhuman servants of a higher authority, a power that even the Overlords bow to.

Jan returns to Earth eighty years later to find a desolate planet. The adults have died off, and the children that are left are linked together in a trance, gradually becoming part of the new race. They use their mental power to strip the Earth of all plant and animal life. Intimidated by their wrath, the Overlords decide their work is done and leave. Jan stays behind to give reports to the Overlords. Eventually, Earth evaporates into nothingness, as though it never existed. The world officially comes to an end in the year 2125.