Sonny (Jeremy Ray Taylor), a fat boy who worships Tesla, and Sam (Caleel Harris), a man with a bit of a brain, are good friends who are often bullied by bad boys at school. On this day, the two were hired by a family to do house cleaning work, and they accidentally found a strange doll Slappy in the attic. Without knowing it, Slappy helped them get rid of the entanglement of the bad boys, and then Slappy helped the two and Sonny's sister Sarah (Madison Iseman) to make trouble in the school. Although benefiting from this weird doll, the three also began to realize the danger and evil hidden under Slappy's evil smile. Slappy, who was rejected, went crazy and decided to turn Halloween upside down... This film is adapted from R.L. Stine's children's literature series "Goosebumps".