Promises is the fifteenth book in the Sweet Valley High series. This book focuses on the death of Tricia Martin, which occurred in the previous book, Deceptions; and continued on from there.

The twins, Jessica and Elizabeth and their family were at the bedside of Tricia Martin, who was dying of leukemia. Jessica was standing away from them, but admitted that Tricia was one of the better members of the Martin family (she had always made her dislike for the Martins known, because of their lower middle class lifestyle).  In this book, Tricia actually passes away here.

A distraught Betsy Martin, Tricia's older sister, came running in, knowing that she had missed saying good bye to Tricia. She had been drinking and was presumed to be high. Steven, Tricia's boyfriend, grabbed the heartbroken Betsy, and comforted her. Mr. and Mrs Wakefield agreed that Betsy should stay the night at their home. Elizabeth was all right with her family's plans, but Jessica was more than horrified.

During her time at the Wakefields, she forges a closer bond with Elizabeth, and shares with her about her artistic talent. Since they were both creative (Elizabeth and her writing; Betsy with her art), they bonded over their common interests.

Jessica, on the other hand, is disgusted with her family taking in Betsy. According to her, Betsy is a no-good tramp who drinks, does drugs and sleeps around with many boys, most of them dropouts and those who hang out at the Shady Lady and Kelly's, two very notorious drinking establishments in Sweet Valley. After an argument with Jessica, Betsy storms off to the Shady Lady, and has only one drink, but Steven and his best friend, Jason, come to her rescue.

Betsy is with Charlie Cashman and Jerry "Crunch" McAllister, at the bar. Charlie is a notorious bully and racist; and Crunch (his nickname from his days as an SVH football player) is already not liked by the Wakefield family, since it was he who crashed his van into Todd Wilkins' motorcycle, injuring Elizabeth and putting her into a coma.

Charlie tried to attack Jason, even after Betsy told him to not cause any trouble, but as a result of his karate training, subdues the bigger boy, and calmly gets Betsy out of the bar.

In the book's second storyline, Winston Egbert is trying to break a pizza eating record. He practices with the school's pizza by eating four of them in 30 seconds; then graduating to try to eat seven extra large pizzas in one sitting at the town's pizza parlor, Guido's. The event was featured on TV in town, and most of his friends gathered to see the feat. Although he didn't break the record, everyone was pleased that he tried to do so.

Betsy later discovered that she had gained a scholarship to a prestigious art school in Los Angeles, thanks to Steven, Jason and Elizabeth who had faith in her and her talent She went back home to be with her father, her only living relative left, but realized that she had new respect for herself and gained a lot of new friends as well.

In a set up for the next book, Rags to Riches, it was revealed that Roger Barrett, who had found that his mom had had a heart attack, had received care from Bruce Patman's father, and was revealed at the end of the book that Roger was the son of Bruce's uncle Paul. Therefore, Roger was now a Patman.

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