When the story begins DuQuesne announces a long absence from Earth, to find another species more knowledgeable than the Osnomians allied with protagonist Richard Seaton.

DuQuesne, by now aware of the 'Object Compass' trained on him, travels far enough to break the connection, then turns toward the 'Green System' of which Osnome is a part.

Seaton is then requested by his allies Dunark and Sitar, the crown prince and prince's consort of Osnome, to repel invasion by the natives of planet 'Urvan', Osnome's neighbor; whereupon Seaton and his millionaire sponsor, Martin Crane, accompanied by their wives and Crane's valet Shiro embark in the spaceship Skylark II to obtain the necessary minerals.

Initially they encounter the Dasorians, an amphibious species of humanoid, who direct them to the Norlaminians, who possess full control of both matter and energy.

[1] Arthur C. Clarke was a fan; the only space battle scene he wrote, in Earthlight, was a specific homage to the attack on the Mardonalian fortress in chapter seven of Skylark Three.