When the child-killing monstrosity, Sid, crawls out of a haunted jack-in-the-box and into her home, Andi must team up with her imaginary friend, Shmoogle; her ever-hungry bulldog, Lady Slobberly; and a mischievous stuffed monkey, Bobo, to stop the monster that her parents refuse to believe exists, despite the fear they feel creeping into their lives.

With her family's life on the line, Andi must use the tools of her childhood, while embracing the dark reality of this monstrous world, to end the monster and save her brother's life, even at the risk of her own.