 One evening the Collins find their maid Mrs. Murdock at the end of their steps: dead, neck broken. Obviously she had an accident. Consequently they need a new babysitter for an upcoming big party. The sensible Helen meets little Evelyn Collins at the discount market and likes her, so she offers to do the job. She doesn t know Evelyn s teenage brother Mark - technically skilled and good in school, but restive and cunning. As soon as the parents have left, he starts psychologically terrorizing Helen and his sister with electronic tricks.