Runaway is the 21st book in the Sweet Valley High book series.
Jessica Wakefield is more than a bit resentful of how things were with her twin sister, Liz. In her mind, Liz could do no wrong while everything she did would end up disastrous. Her resentment would eat away at her, as she thought dark thoughts about her sister.
During this time, she met fellow SVH student, Nicky Shepherd, whose home life was almost as chaotic as her's was. He had made plans for himself to move to San Francisco, where he and a friend of his would be beginning a business. Jessica felt that if she was gone, then things would be better for her family. She then decides that she will do it. She intends to run away from Sweet Valley, and never come back.
The book's b-storyline dealt with Annie Whitman's then-boyfriend, Ricky Capaldo, who was dealing with his mother's denying his grandparents from visiting him. Elizabeth broke through to him and helped him see what the pain he and his mother were dealing with by punishing his father's parents.
Jessica thought it over, and she ended her plans to run away, and returned home. This was the first time that Jessica showed her resentment towards her sister. The second time occurred in book #82, Kidnapped by the Cult.