Despite strange dreams and her ailing father's firm belief in the family lore of a long-ago ancestor's connection to the mythical unicorn, fifteen-year-old New Yorker Elayne remains skeptical until, during a school visit to the unicorn tapestries in the Cloisters, she finds herself entering a tumulteous world where she must fulfill the legacy of her ancestors by taming the unicorn and bringing a tyrant to justice.