Teenager Sarah Quinn (Madison Iseman) lives with her mother Kathy (Wendi McLendon-Covey) and younger brother Sonny (Jeremy Ray Taylor) in Wardenclyffe, New York. Sarah is attempting to get into Columbia University by writing an essay about fear. Kathy agrees to watch Sonny's friend Sam Carter (Caleel Harris) while his father goes out of town. Sonny and Sam are attempting to start a garbage cleanup business, and are called after school to clean up an abandoned house. Inside, they find a locked manuscript and open it, causing Slappy the Dummy to appear. They unknowingly bring him to life by speaking magic words found in his pocket. The book is later stolen by a bully named Tommy Madigan (Payton Wich). At home, Sonny is working on his science project, a miniature version of Nikola Tesla's Wardenclyffe Tower. Slappy then reveals he's alive to Sonny and Sam, and gets their trust by using his magic to do the boy's chores and homework. Meanwhile, Sarah goes to a party to meet her boyfriend Tyler (Bryce Cass), but sees him kissing another girl. Later she arrives home and complains about him to Sonny and Sam, which Slappy overhears. Slappy then proceeds to sabotage Sonny's project..