Slans are evolved humans, named after their alleged creator, Samuel Lann. They have the psychic abilities to read minds and are super-intelligent. They possess near limitless stamina, "nerves of steel," and superior strength and speed. When Slans are ill or seriously injured, they go into a healing trance automatically.
There are two kinds of Slans. One has tendrils and can read the minds of ordinary humans and telepathically communicate with other Slans. The tendrils are golden in color, making it easy to spot a Slan. These Slans are hunted to near extinction. The other type of Slan is tendrilless. They are still super intelligent but do not have psychic capabilities, only the ability to hide their thoughts from the first type of Slan. Kier Gray is the leader of the human society and vows to exterminate the Slans.
As the novel begins, nine-year-old Jommy Cross (a telepathic Slan of the first type) is brought with his mother to the capital, Centropolis. They are both discovered and Jommy's mother is killed. Jommy manages to escape. Jommy Cross is not only the heir to the brilliant inventions of his father, but he represents the last hope of his race to save it from genocide. Because of the importance of his mission, he is opposed by various enemies. Jommy seeks to destroy Kier and in confronting him discovers an astonishing secret: Kier Gray is also a Slan.