The submarine crew in Thresher faces ancient horrors and lurking behemoths within the abandoned underwater geothermal energy facility called Rán Beor. These threats contribute to the growing paranoia and isolation among the crew as they explore the depths.

The main characters aboard the S.S. Thresher include Emily Wodsworth, Daemon Adams, Beatrice “Betty” Callahan, Valerie “Val” Sutton, and Hercules De Baudin. They are a motley crew of troubled individuals venturing into the mysterious underwater facility, each facing personal and external challenges during the mission.

As the crew explores the underwater station, the claustrophobia of the submarine and the terror of the lurking monsters intensify their paranoia. This growing mistrust among cabin-mates leads to tensions and the threat of mutiny, forcing the crew to either unite or perish in the crushing depths.

Rán Beor is the mysterious underwater station that the crew of the S.S. Thresher is sent to explore. It serves as the central location where the ancient horrors reside and where the crew confronts both external monsters and internal psychological struggles, driving the main conflict of the story.

Key moments include the crew members confronting their fears and paranoia, decisions to trust or distrust each other under pressure, and their attempts to navigate the dangers of the underwater station. Specific character actions, such as how they respond to the monsters and manage internal conflicts, critically affect their chances of survival.