We begin the grand story of the unconsidered variable in Hari Seldon's equations, a mutant being of indescribable powers known only as the Mule. He conquers worlds overnight, including the honeymoon destination of Bayta and Toran Darrell. There they meet a clown fleeing from the planet's new lord, the Mule himself. They meet Captain Han Pritcher from the security forces, and eventually the Foundation's greatest scientist Ebling Mis, the man who is the closest to understanding Seldon's psychohistory of any man in centuries. He knows another Seldon Crisis has arrived, and it directly involves the Mule. What will Hari Seldon proclaim in his long awaited return to the Vault?