The Curtain

Pursued by the Curtain, a sort of moving ring that encircles a dead planet, humanity is forced to perpetually circle the globe aboard five ships carrying millions of humans, and relentlessly sends out prospectors to inspect the lands on the horizon to ensure the safety of its nomadic cities. These prospectors, known as "after-guards," are tasked with traveling thousands of nautical miles across the horizon in extremely fast vessels. And as humanity begins its 7,999th revolution, one of them discovers an anomaly near the northern rotational center of the Curtain...