In a world where the human-like Tanu have the upper hand, Elizabeth Orme soon encounters trouble. When they find she possesses rare mind powers, they want her for their own. She won't be used as a pawn in a Tanu versus Firvulag war, but Aiken Drum can't wait to get involved.
Aiken discovers the Tanu's mind-enhancing torcs have given him his own powerful abilities. And it's not long before he devises a plan to challenge the Tanu's leader - for rule of the Many-Coloured Land itself. But another faction seeks the slaughter of all humans, and he stands in their path.
Human time-travelers from the sophisticated Galactic Milieu of the twenty-second century came to the Pliocene Epoch seeking a Garden of Eden. What they found was slavery under the knightly Tanu race, who had been exiled to Earth from a far galaxy. Freed by the usurper Aiken Drum, the humans enjoy a brief period of dominance. But now King Aiken's rule is threatened by the dwarfish Firvulag, who scheme to destroy both humans and Tanu in the nightfall War, a ritual Gotterdammerung that had been postponed when Tanu and Firvulag were banished to Pliocene Earth.
This menace becomes almost incidental when Aiken discovers that his realm is about to be invaded by another human who possesses metapsychic powers even greater than Aiken's own. He is Marc Remillard, the Adversary, instigator of the Metapsychic Rebellion, who nearly conquered the Milieu, and then fled through the time-gate after his defeat. Marc and his surviving followers come against Aiken when it seems that a new time-gate is about to be built—one that will provide a two-way portal between the Many-Colored Land and the future world of the Milieu.
The Adversary, like its predecessors (The Many-Colored Land, The Golden Tore, and The Nonborn King), combines science and fantastic imagery with rousing adventure, humor, and an optimistic view of the human character as it contends against mental and physical perils.
Human evolution makes a quantum leap. And all over the world, people begin to be born with extraordinary minds. Some of them are geniuses and some are very ordinary. But all of these metapsychic operants have mind-powers that "normal" humanity considers amazing—and dangerous.
Intervention paints this advent of Homo superior in a broad and colorful chronicle that begins in 1945 and culminates in 2013. Its many characters reveal the impact of higher mind-powers upon the possessors themselves, upon their "normal" associates, and upon a troubled society striving to avoid nuclear annihilation.
The metapsychic operants are secretive and fearful at first. When they reveal themselves they are regarded with awe, exploited, and finally persecuted. They are torn by the dilemma of what role to play: are they destined to save the "normals" from global war, even if it means that they must use their mental powers to subjugate the race that gave birth to them?
The book's principal protagonists are members of the Remillard family of New Hampshire—whose descendants are featured in Julian May's Saga of Pliocene Exile, a worldwide best-selling quartet that combined science fiction and cerebral adventure. Intervention details with humor, thundering action, and scientific insight a world where the human mind does much more than think—a world that is fantastic, but by no means implausible.