On an Earthlike exoplanet, they obtain "X" from an outcrop almost purely of that mineral; then leave that planet in search of copper. Following an encounter with a "Disembodied Intelligence" (Star Trek's "Q" would later show similar attributes), they enter a cluster of stars nicknamed “The Green System” and locate a planet having copper sulfate oceans. On the Earth-like "Osnome", they befriend the rulers of Mardonale, one of the two factions of the Osnomian natives. When the Mardonalian ruler attempts to betray Seaton and his friends, they find allies in Prince Dunark (a crown-prince of Mardonale's rival "Kondal") and his consort Princess Sitar, whom they later assist in destroying Mardonale. In gratitude, the Kondalians make new copper "power bars" and rebuild the Skylark as Skylark Two, with new weapons known to Kondalian science. Thereafter Seaton's marriage to Dorothy, and Crane's to Margaret, are solemnized by the Kondalian monarchy, and Seaton himself declared nominal "Overlord"