Tegumen is a planet divided between the Red Hat elite on the mountain peaks and the belowers of the valleys with only two or three hours of sunlight each day. The young Yie Evroe is recruited to study galactic energy dynamics at a mountain claustrum community. He falls in love with Joa, daughter of the Red Hat chieftain. The lovers secretly study the archives and discover clues to a different, helial energy system. When the father uncovers their romance, the pair flee down into the valleys. They wander and fi nd refuge among metalworkers of mountain caves., but Red Hat attacks force them to the lowland city where they are sheltered at a folk theater. Final realization of the dream of a practical helial form of power that the valleys can enjoy occurs at Digit Lake, their last refuge.