Lieutenant Georges Corson of the Sun Dominion takes part in the war against the planet Urya. His task is to negotiate with the Beast—an extraordinary being, perhaps even rational—and obtain its help in the war with the Princes of Urya. But as it turns out, the Beast can do a great deal; in essence, it is a living machine of time. Moreover, both it and the small piece of the universe around it can move not only through time but also through space—though it does this unconsciously. In addition, the only specimen available to the people of Earth is pregnant, and after it is landed on Urya, in six months there will already be eighteen thousand Beasts on the planet. After a year, the planet will be engulfed by panic, and the war can be considered won.
But events chose a different path. In near-Earth orbit, the ship explodes, and in order to survive, the Beast moves over a thousand years—accidentally taking with it a piece of space that also includes Corson.
In the future world there are no wild Beasts—only their domesticated descendants, the hypyrons, steeds of time and space. Knowledge of past events and a faithful “conjurer’s mount” allow Corson to influence the past. And he begins to act.