For 60,000 years the five races of the Galactic Milieu have waited for the time when human mental development on Earth is ready for intervention. As the 20th century draws to its end, phenomenal mental powers are displayed by "operants" on Earth. One of these is Rogatien Remillar, book dealer.

All over the world, the metapsychics are honing their skills, learning to stretch their incredible minds far beyond the ken of ordinary humans. Most are dedicated to the harmony of the human soul. But some have darker intentions... If the metapsychics succeed in uniting Earth's minds to take the next step up in human evolution, a place awaits humanity among the alien peoples of the fabulous Galactic Milieu. But if evil minds prevail in their bid for power, Earth will be cut off...and mankind forever doomed!

An origin story of Julian May’s Galactic Milieu Trilogy and a link to her Saga of Pliocene Exile—“a superb piece of speculative fiction” (Library Journal). They have always been among us—the telepaths, the persons possessing higher mind-powers that have been called “metapsychic”—but they have always been few and far between and their abilities weak or erratic. Until now . . . 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 are they destined to save the “normal” 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 worldwide bestselling Saga of Pliocene Exile. 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.