This short story follows a team of human scientists and engineers who develop a high-tech submarine capable of exploring the oceans of Titan, a moon of Saturn known for its liquid methane and ethane. They launch the submarine and begin to explore the depths of Titan's ocean, discovering unique and strange forms of life. As they delve deeper into the ocean, they begin to uncover evidence of an advanced extraterrestrial civilization that once lived on Titan, but also find that the civilization had been wiped out by an unknown cataclysmic event.