The Horror at Camp Jellyjam is a novella written by R. L. Stine. It was first published in 1995 and is the 33rd book in the original Goosebumps book series.
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While on a road trip with their parents, Elliot and his sister Wendy get inside their parents' trailer and crash into a sports camp called King Jellyjam's Sports Camp. The two decide to stay and participate in the activities until their parents can come for them, but while Elliot is enjoying the competitive spirit, Wendy finds it all too bizarre – especially when the winners end up missing, one of the counselors survives a bone-crushing hit to his chest, everyone is disappointed in Wendy who is not sharing their obsessive competitive spirit, and the ground begins to shake at night.