The inhabitants of the British village of Midwich suddenly fall unconscious, as does anyone entering the village. The military establishes a cordon around Midwich and sends in a man wearing a gas mask, but he, too, falls unconscious and is pulled back with rope. The man awakens and reports experiencing a cold sensation just before passing out. The pilot of a military reconnaissance plane is contacted and asked to investigate. When he flies below 5,000 feet, he loses consciousness and the plane crashes. A five-mile exclusion zone around the village is established for all aircraft. After approximately four hours, the villagers regain consciousness, and all are apparently unaffected.
Two months later, all women and girls of child-bearing age in the affected area are discovered to be pregnant, sparking many accusations of both infidelity and extramarital sex. The accusations fade as the extraordinary nature of the pregnancies is discovered, with seven-month fetuses appearing after only five months. All the women give birth on the same day. Their children have an unusual appearance, including “arresting” eyes, odd scalp hair construction and colour (platinum blonde), and unusually narrow fingernails. As the children grow and develop at a rapid rate, it becomes clear they also have a powerful telepathic bond with one another. They can communicate with each other over great distances, and as one learns something, so do the others.
Three years later, Professor Gordon Zellaby (Sanders), whose wife Anthea (Shelley) gave birth to one of the children, attends a meeting with British Intelligence to discuss the children. There he learns Midwich was not the only place affected; follow-up investigations have revealed similar phenomena in other areas of the world.
At age three, the children are precocious, physically and mentally the equivalent of children four times their age. Their behaviour has become even more unusual and striking. They dress impeccably, always walk as a group, speak in an adult manner, and behave maturely, but they show no conscience or love, and demonstrate a coldness to others, causing the villagers to fear and be repulsed by them.
The children begin to exhibit the power to read minds and to force people to do things against their will. There have been a number of villagers’ deaths since the children were born, many of which are considered unusual, and some citizens believe the children are responsible. This is confirmed when the children are seen killing a man by making him crash his car into a wall, and again when they force his suspicious brother to shoot himself.
Zellaby, whose “son” David is one of the children, is at first eager to work with them, trying to teach them while hoping to learn more about them. The children are placed in a separate building where they will learn and live. While the children continue to exert their will, Zellaby is informed that the Soviet government has fired a nuclear shell and destroyed the Russian village that was the only other location on Earth where mutant children still lived.
Zellaby compares the children’s resistance to reasoning with a brick wall and uses this motif as self-protection against their mind reading after the children’s inhuman nature becomes clear to him. He takes a hidden time-bomb to a session with the children and tries to block their awareness of the bomb by visualizing a brick wall. David scans his mind, showing an emotion (astonishment) for the first time. The children try to break down Zellaby’s mental wall and discover the truth a moment before the bomb detonates, consuming the building in flames and killing them all.