The space race between USSR and USA reaches its peak. But suddenly it is interrupted by the third party, the ultimate winner. Colossal spaceships from beyond the Solar system cover all the major cities of Earth. Their owners - the Overlords they call themselves - announce that they have come to bring prosperity and peace to Earth, to end all wars and violence. To fulfill this they take control over all international affairs, slowly integrating their will not only into political but into cultural and educational layers of human life.
Of course, despite the major countries and their government had no option than to obey, the resistance emerged almost immediately. Desperate people, calling themselves “The Freedom League” don’t trust aliens, no matter how benevolent they seem to be. They form something resembling a ruthless terrorist organisation of planetary scale, but the members of the League consider their goal noble enough to justify this. They are fighting for humanity, its free will and against the oppressors, after all.
The intervention is led by “The Supervisor”, the leader of the Overlords. The Supervisor talks only to U.N. Secretary named Rikki Stormgren, sharing with him his plans to create an ultimately happy community all over the world. Slowly Stormgren and the Supervisor befriend each other (as much as it is possible for such a different entities as human and Overlord). The Supervisor even reveals to him his true name - Karellen.
Meanwhile The Freedom League decides to eliminate the only person between the Overlords and the other people. They kidnap Stormgren to interrogate him before and to learn as much as they can about the aliens. But Rikki himself doesn’t know much except that the Overlords are really benevolent. He even has never seen Karellen in person.
Soon Karellen rescues him, sending robots to extract Stormgren from his prison. But after the talk with resistance members, Rikki thinks all that happened over. He understands that he is nothing more than a useful instrument for Karellen and now tries to learn more about the Overlords himself. At first, he asks Karellen to show in person, but the Overlord replies that humans are not yet ready to see them. He promises that aliens will show themselves 50 years after. Stormgren, knowing he won’t live that much, isn’t satisfied with this answer. He asks a scientist, Pierre Duval, to help him see the Overlord. He uses the bright light to briefly glimpse at what Karellen looks like, but Rikki is so confused by that sight that he never tells anyone about his discovery.
There are some more revolts, but the Overlords deal with them with the same patience, treating the rebels as silly kids and trying not to make any harm to anyone. Rikki retires and finally dies, observing the changes in society he never even dreamt about. He doesn’t tell anyone a thing about Overlords’ appearance, even on his deathbed.
Second book starts from the events years after his death. The Overlords kept their promise and revealed their looks to humans. They look like the iconic Christian demons with horned heads, leather wings, tails and reddish-black skin. But it almost doesn’t matter anymore, because all religions are almost forgotten, the remnants are just cultural heritage without any spiritual meaning. Humans live in blissful happiness as a single worldwide community. Greed, jealousy, anger are gone, everyone is just enjoying life in the ways he wants to. This period is called The Golden Age.
A man named Rupert Boyce organizes a party. Amongst the invited are George Greggson, Jean Morrel and Jan Rodricks. Also an Overlord named Rashaverak comes to the party to study the Boyce’s library. Rupert is well-known for studying and collecting evidences of paranormal events and Rashaverak, as other Overlords, is for some reason thrilled with it.
At the end of the party they try to conduct a spiritualistic session when Jan suddenly asks where the Overlords’ homeworld is situated. He receives an answer and when later he checks it with his fellow astronomers, this answer seems to be correct. Now Jan is obsessed with finding that planet to see what the real life of the Overlords look like. His another friend, an oceanographer named Sullivan comes with the plan. He suggests to hide Jan, drugged almost to comatose state, in the Overlords’ supply ship. But when (and if) Jan returns home, eighty years will pass, so no one of those he knows now will be still alive. Jan agrees anyway. He curls inside one of the statues portraying human culture and fauna that the Overlords ask to make for them - a giant blue whale - and goes to the deep sleep.
Karellen learns about this plan. He doesn’t interfere, but once again speaks to the world, telling the humans about Jan’s plan and saying that he is the last human to leave Earth, because their specie isn’t prepared for what awaits in the deep space. Humans may be able to control their planet, their solar system, but they are still too weak for the distant stars.
Meanwhile, Jean and George get married and now have two children. They move to the New Athens, an artistic colony on the small island. The members of the colony dedicated themself to creating works of art, writing, drawing, sculpting and trying to preserve the gift of creation humanity has. Overlords brought to Earth not only peace and happy life, but also stagnation, because there are no more problems to deal with and no more needs to put creativity into.
Once Jeffrey - one of their kids - is playing on the beach when the tsunami hits the island. But the boy hears a mysterious voice that guides him to safety. He tells his father about what happened and George is almost sure that it was the voice of Overlord. But he doesn’t know why his son was chosen to be saved.
A few days after the tsunami Rashaverak comes to visit the family. He says that it was just a friendly visit, but George clearly sees that he is looking at Jeffrey too attentively. Later he and Jean start to notice something strange in their kids. Both Jeffrey and his baby sister Jennifer start seeing strange prophetic dreams about distant worlds known only to Overlords, develop telepathy and telekinesis, casually lifting their toys in the midair or reading thoughts of their parents. Other kids on the island - and all over the world - start showing the same signs soon after him. The younger they are the stronger are their powers and the less human are their ways of thinking.
Rashaverak meets the family again and explains that Jeffrey and Jennifer do not belong to the parents - or even humankind - anymore. They are ready to become a part of Overmind, the entity that exists in the Universe scale and absorbs every developed civilization into it. The only one who are spared are Overlords, their mission is to find civilizations that are about to transform and prepare them for transcendence. Rashaverak says that only the new generation will be able to unite with the Overmind, other humans are not needed anymore. They will become barren and extinct, leaving their last generation to their fate. Jeffrey was only the first to come, the first neutron in the chain reaction that will transform humans into something else.
The Overlord asks George and Jean to be happy with their kids while they still can, because soon they will be taken away and won’t be anything even vaguely resembling humans. Instead of wrath and despair George feels sorry for Rashaverak, he sees that Overlords are suffering because of inability to follow the humanity. They are just an instrument of Overmind, they saved their personalities but as a race they have no future, they are stagnant, existing only to obey the Overmind and search for new races to transcend them.
Karellen makes a final speech to the humanity. He says that their job on Earth is done. They came here a century ago to prevent humans from destroying themselves in wars and driving them away path available only to several races in all the Universe - brave, curious and energetic enough to continue developing and uniting science and paranormal. By creating utopia on Earth the Overlords ended all the development of human race, not allowing them to mess with the force it doesn’t understand.
Karellen also says that humans remember them well. The Overlords have come to Earth ten thousand years ago to study humans and learn that they indeed are capable of incredible things by sheer energy of their psychic. But the minds of the first cave people in their sudden prophetic insight, realized that the Overlords will come again at the end of times. The image of the Overlords was imprinted in the collective unconscious as the embodiment of evil, devils, demons.
So the Overlords now just guide humanity, letting the whole race to develop its powers and finally create the new generation ready to ascend and join the Overmind. The Overlords themselves are just mere observers, they, so much more developed intellectually, can’t comprehend humans and can just record this great experiment held by Overmind.
Karellen says that his duty is to protect the last generation from the other humans, maybe even from their parents mad from despair. He says that he will take away all the children younger than ten years to the distant continent. Karellen adds that destroying humanity, as putting a mortally wounded animal out of its misery, would be a mercy, but he isn’t allowed to do this. So the humans are free to choose how to live their last years.
The author returns to Jan who is taken to the Overlord’s homeworld. There are lots of things that are unknown to him. Overlords are neutrally friendly but they almost don’t understand him, and Jan doesn’t understand them. The only thing that seems familiar for him is the museum of the foreign civilizations. The statue he travelled in was meant for this museum.
The Overlords study him, experimenting - though harmlessly - on him. But Jan himself sees something strange, a place, resembling a mountain that changes its color, and understand that this “mountain” uses colors to communicate with the Overlords - and to give them commands.
Soon after that discovery Jan is returned home. But the Earth is already empty. Some people (as colonists in New Athens who blew the nuclear bomb on their island) committed suicide, other fought against the Overlords becoming more and more barbaric and primitive. Several communities tried to live their life peacefully, growing old and dying quietly. Nevertheless there are no humans to greet Jan.
Rashaverak tells him the story that happened on Earth. He accompanies Jan and helps him to stay psychologically stable. At the same time he studies the last human available, hoping that the knowledge he gets will once help the Overlords to ascend as humans do.
Jan learns to play the piano and masters the instrument during the years he is the last human on Earth. Rashaverak shows him the children - dirty, almost naked as the primitive tribes, dancing in strange circles all over the continent. They don’t resemble humans anymore, though their faces still can be recognized, there are no expressions on them. Jan says that even the corpses save something from their previous lives but these kids are totally blank. Rashaverak agrees, adding that the kids don’t have personalities anymore, the Overmind teaches them - or it - to become part of itself.
After years of dancing, the kids just evaporate every life on the continent they are on. Later, they shift the Moon, tidally unlocking it and, as a result, the Earth slows down. Rashaverak says that it’s time for them to leave because it is dangerous to stay near this entity. He offers Jan to leave with them, but he decides to stay and share the fate of his planet. Then Rashaverak asks him to observe and report everything he sees until the last moment. He wants to get as much knowledge from dying race as he can.
Jan agrees. He stays in the one of the research centre of the Overlords, seeing as the children leave their physical bodies ascending to the sky as a giant tree of light. He is glad that the Overmind left the Moon on its place - Jan feels better looking at it.
Then the gravitation starts to disappear, so does the atmosphere. The last words of Jan are about the Earth becoming transparent and dissolving, while the new part of the Overmind devours it.
From beyond the orbit of Pluto Karellen looks at disappearing Earth giving honor to the humankind and hoping that one day his race will be able to follow its steps.