At the beginning of the story, the antagonist Lone Power, creates a surge of Dark Matter, called "the Pullulus", whereby the Senior Wizards lose their wizardry and only wizards before adulthood remain to oppose him. Seeking an 'instrumentality' conferring advantage on its discoverer, protagonists Ponch, Nita, Kit, Ronan, Filif, Sker'ret, Dairine, and Roshaun identify it as a 'Hesper': a benevolent alter-ego of the Lone Power himself. This 'Hesper' is discovered in one 'Memeki': a coleopteron native to planet 'Rashah'. Before she can agree with their cause, they are captured by the Lone Power, who suppresses all wizardry in the area; whereupon Ronan sacrifices himself to free the One's Champion from his mind, who restores wizardry and allows Memeki to assume command of the planet. With Ronan near death and the Pullulus advancing towards Earth and Filif's home planet, the protagonists join a gathering of all Earth's remaining active wizards, to stop the Pullulus. As the Pullulus advances, Roshaun channels solar matter to burn the Pullulus, but himself vanishes when the energy exceeds his strength. Challenged by Ponch, the Pullulus assumes a wolf-like shape and Ponch becomes a canine incarnation of the One, which vanquishes the Pullulus and departs. Most of the survivors (including Ronan) return to Earth, where wizardry is restored to the seniors, and Ponch is glimpsed in a stray sheepdog; while Dairine visits Roshaun's parents to train as his successor.