Dan is a confident college student and champion trampolinist at the University of California, Berkeley. Despite his outward athletic achievements, he struggles with deep inner turmoil and a profound fear of mortality, resulting in severe insomnia. His restless nights lead him to an all-night gas station, where he begins rigorous mental and physical training to become a "peaceful warrior."

Socrates is an enigmatic, white-haired man in his fifties or sixties who works as a gas station attendant. Dan gives him the nickname "Socrates" due to his philosophical nature and cryptic life lessons. He practices martial arts, possesses deep intuitive abilities, and lives a remarkably simple life while teaching his students how to free their minds from illusions.

Joy/Joyce is a young woman who studies under Socrates. She embraces a peaceful, warrior-like attitude that contrasts sharply with Dan's internal distress. She frequently engages in physical training, such as T'ai Chi and running in the hills, and she approaches life's unpredictable moments with a calm, accepting mindset.

Joseph is a café owner who previously served as Socrates's cook and personal attendant. He lives according to the spiritual and dietary principles taught by the old man. He offers practical support to Dan during his strict fasting and discipline phases, specifically assisting him with proper breathing techniques.

Linda is a woman Dan dates while trying to balance his normal collegiate life with his intense spiritual training. She represents the conventional world and offers Dan a chance at ordinary intimacy as he works to apply Socrates's lessons to daily human relationships.

Valerie is a medical professional who assists in Dan's care. She and Dan share a brief, impulsive sexual encounter during a period when Dan is supposed to be practicing strict discipline and fasting under Socrates's orders.

Donald is a distressed young college student who is on the verge of taking his own life. He appears to Dan in a powerful, guided vision orchestrated by Socrates, serving as a direct reflection of Dan's own mental health struggles and despair.