Millennia after a thermonuclear holocaust decimates civilization, the myriad, mutated children of Earth spread their wings and colonize the galaxy's near reaches. Imperium Terrestriana, loosely governed by an elite neo-human minority, fosters Convention, the body of civil law featuring reborn Code Duello, a custom that allows interpersonal affairs to seek unnatural equilibrium as trillions of eligible patricians and plebes wield their swords to settle private disputes. Explorers on the empire's parsecs-distant periphery discover Dan, an idyllic, green and golden planet ripe for colonization, where enigmatic, supposedly ancient indigenous aliens of superior intellect come and go like shadows, yet lack habitations or an infrastructure. Disapproving of violence, the Danii observe askance as colonization begins in earnest, and are horrified when sequestered convicts, violators of Convention, begin to arrive and duelists vanish before the eyes of terrified colonials. When questioned, the Danii repeatedly explain how mysterious beings referred to as "Higher Ones," vastly displeased by the wanton destruction wrought by victorious duelists, have taken the miscreants "into their gentle care." The unseen Higher Ones eventually make their acute displeasure known via precipitate action, leading to a chilling, ironic climax that raises provocative questions about neo-humankind's place in the eternal scheme of things.