A friendly troll with a magic green thumb grows one flower too many for the queen, whose laws require all trolls to act meanly, be ugly and scare humans whenever possible. As a punishment, he is exiled to a world of concrete, where he should live a life of proper trolldom: Manhattan. But of all places, his pod lands in Central Park, where he feels right at home. He befriends a young brother and sister, out for the day unknown to their parents, and must immediately protect them from the queen's attack. In the process, the boy learns responsibility, and the unpopular queen is overthrown.