In the age of "Aquarius," a time of harmony and understanding, a tribe of hippies gathers onstage. George Berger, the tribe's most expressive member, addresses the audience directly and explains that he seeks his ideal woman ("Donna"). Members of the tribe mock racism ("Colored Spade") and celebrate diversity ("I'm Black").
Claude, the moral center of the group, explains his dream of living in "Manchester, England" while others lament - or brag about - their lack of privilege and possessions ("Ain't Got No"). Sheila Franklin, an NYU student and antiwar protestor, declares "I Believe in Love," and Jeanie, an idealistic, pregnant environmentalist, satirises the world's deteriorating "Air."
Berger recounts his recent banishment from high school in "Goin' Down." Claude reveals that he has been drafted, but he and Berger choose to reject their draft notices, and instead celebrate their "Hair." ("Give me a head with hair, long beautiful hair, shining, gleaming, steaming, flaxen, waxen...")
Sheila gives Berger a new yellow shirt, but he cruelly spurns her gift. She reminds him that he's quick to feel empathy for the masses, but he comes up short in personal relationships ("Easy to Be Hard").
As the flower children are leaving to attend a Be-In, one girl, Crissy, alone in her thoughts, sings of a boy she once met and of her longings to meet him again ("Frank Mills"). At the "Be-In," the boys all burn their draft cards in an anti-war demonstration. Claude begins to toss his card to the fire, but changes his mind and removes it, wondering how he fits in to this changing world ("Where Do I Go?").
During a drug-induced hallucination ("Walking in Space"), Claude visualizes George Washington retreating, Indians shooting white men, famous American characters being attacked by African shamans, Abraham Lincoln patronizing American slaves, and stylized mass murders. After the violence, Claude sees his parents and a sergeant beaming with pride over his enrollment in the U. S. Army. They fade from view, replaced by the flower children who turn into horrible monsters and start killing one another; directing their aggressive actions towards Claude ("Three-Five-Zero-Zero"). Two tribe members, observing this scene of destruction, wonder "What a Piece of Work Is Man."
Claude realises that once he's inducted into the Army, he will miss all of life's simple pleasures ("Good Morning, Starshine" and "The Bed"), and he exits with a feeling of doom "Ain't Got No (Reprise)."
Claude soon re-enters, stiffly dressed in a military uniform, but his friends are unable to see or hear him as he sings of his regrets ("The Flesh Failures"). Separated from his tribe and presumably killed in the war, Claude lies on his back, motionless. The tribe, seeking hope in the wake of loss, sings "Let the Sun Shine In."