In a distant future, the planet Amoi is governed by an advanced computer called Jupiter. The population is largely male, and a privileged light‑haired elite may temporarily own dark‑haired "mongrels" as companions. One elite, Iason, meets a mongrel named Riki in the lower districts and brings him home. Yet Iason retains Riki beyond the accepted period, sparking whispers of a possible bond between them within the tightly regulated society and the elite's reputation at stake.