After World War II, Freddie Quell, a former Navy man, struggles with his traumatic wartime experiences and unsettling sexual urges, leading to erratic behavior and a drift through various menial jobs. His volatile nature is exacerbated by an addiction to making and consuming toxic homemade alcohol. Freddie's journey is one of constant unease, as he wrestles with his psychological demons, unable to settle into post-war society or sustain meaningful relationships. His restlessness is a sharp contrast to the optimism and economic boom enjoyed by many in postwar America.

During his nomadic wanderings, Freddie stumbles onto a yacht where he meets Lancaster Dodd, the charismatic leader of a philosophical movement known as "The Cause." Dodd, intrigued by Freddie's troubled psyche, takes him under his wing, believing his methods and teachings can help Freddie overcome his past. As Freddie becomes more involved with "The Cause," he develops an intense bond with Dodd, who becomes a mentor figure. However, the group's unorthodox practices and Dodd's enigmatic nature set Freddie on a path of self-discovery that challenges his understanding of the world and his place within it.