Set in a near-future earth, the west and the east have been at war for more than a decade, and resources are running thin. The west is stealing oil from the east with specialized nuclear submarines (subtugs) that sneak into the underwater oil fields of the east to secretly pump out the oil and bring it back. With a crew of four, these submarines undertake the most hazardous, stressful mission conceivable, and of late, the missions have been failing, with the last twenty submarines simply disappearing.
The east has been very successful planting sleepers in the west's military and command structures, and the suspicion is that sleepers are sabotaging the subs or revealing their positions once at sea. John Ramsay, a young psychologist from the Bureau of Psychology (BuPsych), is trained as an electronics operator and sent on the next mission, replacing the previous officer who went insane. His secret mission is to find the sleeper, or figure out why the crews are going crazy.
Typically for Herbert, psychology and religion play a large role in the narrative, as Johnny comes to understand the nature of the subtug crews and how they carry out their missions.