Kidnapped by the Cult is the 82nd book of the Sweet Valley High book series. In this story, Jessica is furious with her family and friends after having been grounded, and, in a bid to get some much needed attention, almost ends up joining a cult.
In the previous book, Rosa's Lie (SVH #81), Jessica is grounded for two weeks by her parents when they discover that she had let her math grade take a nose dive, and was in fear of failing the course. When this book begins, Jessica is listening despondently to her friends rehashing the weekend's parties they had at Lila's house. Jessica was even more resentful (due to the fact that she had been grounded beginning with the Pi Beta Alpha induction ceremony and dance) because Lila and her friends were talking about the fun weekend non-stop.
She was also infuriated with Elizabeth for telling her parents about her math issues, and in general, feels resentful of how good Elizabeth was and how bad she was (a similar case to SVH #21 Runaway). And she is also infuriated with her boyfriend, Sam Woodruff, who is more interested in his motorbiking contests than being with Jessica. Her final week of grounding was hard, the only extra-curricular activity she could continue was cheerleading, and the cheerleaders rubbed it in about her being grounded. (As she was changing into her cheerleading outfit, Lila makes a snide comment related to Jessica being grounded, and she nearly snares her snobbish frenemy's hair in the locker door, when she slammed it)
On her day of being ungrounded, she forgets that Sam had a dirtbike rally, and he wanted her to cheer him on, but a furious Jessica tells him off and drives off to the mall herself. She was angry at how her family and friends were just so self-centered and self-absorbed and didn't care about how she felt; as such, she flings herself on a bench in the mall and cries.
A concerned young man named Ted sees her in distress and offers her friendship with a group called the Good Friends. They lived in a run-down house on Cedar Street, in one of the least desirable parts of Sweet Valley, but the outside of the house masked a cheerful interior which surprised Jessica.
She meets most everyone in the group, Ted, Sky, Annie, Agnes, China, and a woman named Susan, who was very hostile and resentful towards her. But the instant that she meets the group's head, Adam Marvel, she is immediately entranced and feels at home with him.
She becomes a regular attender of the meetings, and eschews her former life, cheerleading; hanging out with Lila and Amy Sutton and her other friends; and even skipping out on dates with Sam to hang out with the Good Friends. Due to Adam's influence, she cleans her room; begins to dress a bit more conservatively and reads a lot more, mainly books by Adam Marvel.
Her family is concerned, because it was revealed that Adam's group was a cult, which had a tendency to be using charities to make money for himself. It was also revealed that Adam is a manipulative and duplicitous man who uses his charm to sway teens away from their families. His anger is revealed, especially when one of the Good Friends, a boy named Brian is taken from the group by his parents who didn't much like what Adam Marvel stood for. He was afraid that he would be called back to Sweet Valley to testify about Adam's criminal dealings.
In a panic, lest his scheme should be undone, Adam decides to leave Sweet Valley, and almost takes Jessica with him! The group takes down everything and packs things in a van. Jessica is so swayed by Adam's praise and his friendship that she sees that she ought to go with him.
Elizabeth, arriving with Sam and Todd, pleads to Jessica to listen to them, but their beseeching still falls on deaf ears, until Sam brings out Susan, who was revealed to be a reporter who had infiltrated the Good Friends, to show that Adam Marvel was a fraud. He had attacked her, knocking her unconscious; and he had bound and gagged her, and had planned on leaving her for dead, while he and the rest of the cult had left Sweet Valley to move on to another town. Eventually, Adam was arrested for embezzlement and the attack on Susan; the cult was apparently disbanded, and Jessica's life returned to some semblance of normalcy.