12-year-old Ted Wiggins lives in Thneedville, a walled city where everything is artificial, with no living plants ("Thneedville"). Ted has a crush on environmentalist Audrey, and decides to impress her with a "real tree". His grandmother Norma tells him the legend of the Once-ler, who knows what happened to the trees. Leaving Thneedville in search of the Once-ler, Ted discovers that the outside world is a barren, contaminated wasteland. He finds the Once-ler, who agrees to tell him the story of the trees over multiple visits. Returning home, Ted encounters Thneedville's greedy mayor, Aloysius O'Hare, whose company sells bottled oxygen to the polluted city. Explaining that trees, and the oxygen they produce freely, pose a threat to his business, O'Hare pressures Ted to stay in town, but Ted continues to visit the Once-ler.
