Venturing into intricate cave systems, the deep oceans, and subterranean aquifers where light barely reaches, we meet the scientists who have dedicated their lives to creatures who have evolved in perpetual darkness, working tirelessly—often in obscurity—to understand and protect ecosystems and animals most people will never know exist. Paralleling the deeply personal journey of the film's director as he confronts a terminal illness, the story becomes a reflection on what it means to face one's own darkness.