Goosebumps 2: Haunted Halloween follows Sarah Quinn, her younger brother Sonny, and their mother Kathy as they become caught up in a spooky adventure. Sonny and his best friend Sam, known as the "Junk Brothers," collect unwanted items for extra cash. While searching through discarded junk, they accidentally unleash Slappy, the mischievous ventriloquist dummy from an unpublished Goosebumps story.