Traveling Companion Wanted

A spaceman is accidentally propelled from a staged hull-repair into the ocean and falls through a funnel-shaped crater into a subterranean passage. After disentangling himself from malfunctioning gear he drifts and then uses limited propulsion to follow a narrowing channel where blind, abnormal sea creatures, floating wreckage, mud turning to rock, and a swift central current complicate travel. Relying on improvisation and endurance, he navigates the strange undersea river, endures disorientation and physical strain, and ultimately completes a prolonged, difficult passage to an unfamiliar shore.