Mindy Evans celebrates the night before her eighteenth birthday by attending the Carson High School dance with her boyfriend Bill. They wander outside among the couples who are kissing and smoking marijuana, but Mindy continues to rebuff Bill’s physical advances. She returns to the dance, where young teacher Jack Thompson, an amateur photographer who is shooting the dance for the school paper, takes her picture. Horrified because she has not combed her hair, Mindy asks for the photo’s negative so she can destroy it, and Jack agrees to give it to her later. Soon after, Jack’s wife Gretchen, the school gym teacher, complains about the music and stalks out in anger when Jack does not want to leave early. Later, a pair of students fall into the pool while fighting, inspiring the rest of the students to jump into the water gleefully. At home, Gretchen refuses to drink with Jack, then rebuffs him sexually. The next morning, while Mindy’s best friend Sandy surreptitiously plans a surprise birthday party for her for that evening, Mindy visits Jack to retrieve the photograph. Spotting naked snapshots of Gretchen, Mindy encourages Jack to practice photography professionally and suggests herself as a model. Although Jack tries to decline, Mindy, who loves attention, flirts aggressively, and he finally gives in. They drive up the California coast in Bill’s car, which Mindy has borrowed, and once in the mountains spot a trio of hippies bathing nude. Mindy runs to join them and Jack, at first reluctant, follows. Hours later, they all go back to the house of one of the hippies and, after eating some brownies, Mindy kisses Jack passionately. At the same time, Mindy’s friends have gathered for her party and are shocked when she does return home that night. The next morning, Mindy refuses to reveal where she spent the night, and Bill declines to push the issue. Soon after, she asks Jack to meet her at the beach, where she reveals to him that the brownies were laced with marijuana. Frustrated by his attraction to her, Jack insists that they stop seeing each other, and she runs away, hurt. Days later, when Jack tries to plan his summer vacation with Gretchen, she informs him she plans to visit her sister alone. Meanwhile, as Bill and his best friend Les, who is Sandy’s boyfriend, work on their dragster cars, Les reveals that Mindy has told Sandy that she has a crush on Jack. Mindy has grown disillusioned with middle-class trappings, and at a sleepover with Sandy, complains that having money and a good job are pointless, citing Sandy’s alcoholic father as an example. When Jack calls pleading to see her, she relents, and over the next weeks, they have several romantic rendezvous. Eventually Bill hears about their meetings, and on the school athletic grounds, tosses a basketball at Jack to taunt him. After Jack throws it back forcibly, in the gym shower the female students discuss the incident, gossiping about Jack’s bad marriage. Mindy, who has overheard, reveals to Sandy that she is pregnant, then informs Jack. Soon after, he gets drunk and confesses to Gretchen, who immediately leaves him, then calls his doctor, who has examined Mindy and now counsels Jack to sedate her so she does not harm herself. That night, Bill and Les enter a drag race, during which Bill narrowly avoids disaster and wins his race. Mindy borrows his car and drives off with Sandy, and by the side of the road picks up Pan, one of the hippies from Mindy’s first night with Jack. Jack has attended the races looking for Mindy, and now enlists Bill and Les to search for the girls. Mindy soon runs out of gas and convinces Sandy and Pan to hitchhike to Big Sur, leaving a note on the windshield in lipstick. The trio is given a ride and dropped off in a small town, where they steal food from a bakery, then accept rides from a gang of bikers. Although the men at first seem good-humored, they stop at a pool hall and proceed to terrorize the owner. After starting a fight, they grab the girls and Pan and drag them out into the woods, where they beat Pan into unconsciousness. The men then caress Sandy with a knife and force pills down her throat, but the girls break free and race through the woods in the dark, followed by the men on their bikes. As the girls hide in a barn, Jack and the boys find the car and, after informing to the police, head to Big Sur in pursuit. The next morning, the girls travel back to the main road just in time to see Pan being rescued by a policeman. Spotting one of the bikers’ abandoned motorcycles, Mindy insists on riding it to Big Sur, and Sandy reluctantly joins her. The police soon discern that the girls have taken the bike, and report the information to Jack, who follows with Bill and Les. The girls travel all day, fleeing a diner when they cannot pay for their meal and evading several amorous strangers. An hour outside of Big Sur, Jack and the boys wait at the police station while the girls sleep on the beach. Noting a commune gathering nearby, Mindy and Sandy join the growing audience of a charismatic hippie preaching purity of thought. Just then, the police arrive to break up the meeting, believing the commune leader to be a drug dealer. As Mindy and Sandy are taken in by the police, Jack learns from his doctor that Mindy is not pregnant. Weeks later, Mindy and Sandy attend the Carson graduation. Gretchen, impressed with Jack’s involvement in rescuing the girls, hugs him. At the graduation dance that night, Les and Sandy break up amicably and Bill informs Mindy that he has been accepted to MIT. After kissing him goodbye, Mindy meets the school’s newest teacher, Mr. Fletcher, and is soon dancing with him suggestively.